I'll help you out, which way did you come in?
Hard one to do, main problem is some content creators list the correct category, others merely tag locos as "miscellaneous" so they don't show up in the category search. Setting the TS12 content manager filter for built in = true, obsolete = false, category = locomotives, I get this;
Acela Express, Power Car (front),<kuid:9:1>
Acela Express, Power Car (rear),<kuid:9:2>
Amtrak AEM-7 Acela Paint,<kuid:87854:982511591>
AN GM Class,<kuid:-1:100013>
AN 830 Class,<kuid:-1:100737>
AN 930 Class,<kuid:523:1046>
ATSF B40-8W,<kuid2:45324:110015:1>
ATSF C30-7,<kuid2:45324:100022:2>
ATSF F7A,<kuid:-1:1>
ATSF F7B,<kuid:-1:100135>
ATSF GP60B,<kuid2:45324:100061:1>
ATSF GP60M,<kuid2:45324:100060:1>
ATSF SD40-2,<kuid:-1:100871>
ATSF SD45,<kuid2:45324:100140:1>
Austrac 48 Class,<kuid:523:1056>
BN SD40-2,<kuid:-12:3537>
BR Class 105 DMB,<kuid:79563:10501>
BR Class 105 DTCL,<kuid:79563:10502>
BR Class 13 Master,<kuid:2512:1131>
BR Class 31- Blue,<kuid:79563:10391>
BR Class 31- Blue (weathered),<kuid:79563:10394>
BR Class 313 DMSO Blue & grey,<kuid:343177:313001>
BR Class 37 Blue,<kuid2:2512:2371:6>
BR Class 37 Blue (Split Headcode),<kuid2:2512:2374:7>
BR Class 47 blue,<kuid:79563:1185>
BR Class 47 blue- silver roof,<kuid:79563:1226>
BR HST 125,<kuid:-1:100039>
B&O F7A,<kuid:-1:100117>
B&O F7B,<kuid:-1:100118>
CHN DF11G 0001 Shanghai Dpt.,<kuid:798180:100020>
CHN DF11G 0002 Shanghai Dpt.,<kuid:798180:100028>
CHN DF11G 0005 Beijing DPT.,<kuid:798180:100029>
CHN DF11G 0006 Beijing DPT.,<kuid:798180:100030>
CHN DF11G 0101 Guangzhou DPT.,<kuid:798180:100031>
CHN DF11G 0102 Guangzhou DPT.,<kuid:798180:100033>
CHN DF11 0001 test loco,<kuid:276266:100032>
CHN DF11 0018 Shenzhen depot GZ,<kuid:276266:100036>
CHN DF11 0056 Shanghai Depot SH,<kuid:276266:100031>
CHN DF11 0099 Shanhaiguan Depot SY,<kuid:276266:100040>
CHN DF11 0111 Hangzhou Depot SH,<kuid:276266:100042>
CHN DF11 0237 Jiayuguan Depot LZ,<kuid:276266:100037>
CHN DF11 0414 Sankeshu depot HRB,<kuid:276266:100029>
CHN DF11 0418 Western Beijing depot BJ,<kuid:276266:100038>
CHN DF11 0422 Urumqi Depot,<kuid:276266:100035>
CHN DF7C custom numbers A,<kuid:276266:1182>
CHN DF7C custom numbers B,<kuid:276266:1188>
CHN DF7C 5221 Harbin Depot,<kuid:276266:1173>
CHN DF7C#5013 Shanghai Depot,<kuid:276266:1111>
CHN DF7C#5192 Chengdu Depot,<kuid:276266:1180>
CHN DF7C#5423 Chengdu Depot,<kuid:276266:1165>
CHN ND5-1(GE C36-7),<kuid:276266:1062>
CHS4-052,<kuid:293699:22052>
CHS4-069,<kuid:349860:124001>
CHS8-008 A,<kuid:432925:55>
CHS8-008 B,<kuid:432925:56>
CHS8-009 section 1,<kuid:354694:8910030>
CHS8-009 section 2,<kuid:354694:8920030>
CHS8-013 section 1,<kuid:354694:8910013>
CHS8-013 section 2,<kuid:354694:8920013>
CHS8-036 section 1,<kuid:432925:1106>
CHS8-036 section 2,<kuid:432925:1107>
CHS8-041 A,<kuid:432925:50>
CHS8-041 B,<kuid:432925:51>
CHS8-052 A,<kuid:432925:32>
CHS8-052 B,<kuid:432925:33>
CHS8-056 A,<kuid:432925:52>
CHS8-056 B,<kuid:432925:53>
CHS8-065 A,<kuid:432925:13>
CHS8-065 B,<kuid:432925:14>
Class 26 0 Blue,<kuid2:51536:26100:2>
CN FPA4,<kuid:-1:100150>
CN SD40-2,<kuid:-12:3534>
CP FPA2,<kuid:-1:100153>
CP FP7A,<kuid:-1:100121>
CP F7B,<kuid:-1:100122>
CR GM Class,<kuid:523:1038>
CS7-140 A,<kuid:432925:86>
CS7-140 B,<kuid:432925:87>
CS7-141a,<kuid:361619:50>
CS7-141b,<kuid:361619:51>
CS7-224A,<kuid:475776:100423>
CS7-224B,<kuid:475776:100426>
C&O F7A,<kuid:523:1082>
C&O F7B,<kuid:523:1084>
Deltic BR blue,<kuid2:146848:10200:2>
Deltic 'Racehorse,<kuid2:146848:10220:3>
DM62-1804,<kuid:361619:24>
DRGW F7A,<kuid:523:1083>
DRGW F7B,<kuid:523:1085>
Enafer DL500,<kuid:-1:100825>
ER FA1,<kuid:-1:100143>
FEPASA RSD-8 TIM,<kuid:523:1058>
f7,<kuid:-10:189>
GP9P N&W 500 maroon,<kuid:45588:1410>
GP9P N&W 512 maroon,<kuid:45588:1413>
GP9P N&W 620 maroon,<kuid:45588:1414>
GP9 N&W 640 black,<kuid:45588:1415>
GP9 N&W 781 black,<kuid:45588:1416>
HOTT MAV Bzmot,<kuid2:9999:132:3>
HOTT MAV V63 alt2,<kuid2:9999:8:2>
HOTT MAV V63 XXX,<kuid2:9999:6:2>
HOTT MAV V63 010,<kuid2:9999:22:1>
HOTT MAV V63 014,<kuid2:9999:23:1>
HOTT MAV V63 018,<kuid2:9999:24:1>
HOTT MAV V63 025,<kuid2:9999:25:1>
HOTT MAV V63 034,<kuid2:9999:26:1>
HOTT MAV 6342 Desiro Unit A,<kuid2:9999:150:3>
HOTT MAV 6342 Desiro Unit B,<kuid2:9999:151:3>
IR SD40-2,<kuid:523:1094>
Loco UP 0-6-0 #4609 TS2010,<kuid2:69871:2061:2>
LV FA1,<kuid:-1:100144>
MAV M41,<kuid:9999:3>
MAV M44.4,<kuid:9999:119>
MAV V43 FGVEK,<kuid:9999:111>
MAV V43 OR--K,<kuid:9999:159>
MML HST New,<kuid:61109:10118>
MML HST weathered,<kuid:61109:109>
MML_HST,<kuid:61109:108>
MN Bombardier M7A,<kuid:523:100062>
MN Bombardier M7B,<kuid:523:100050>
MN FL9,<kuid:311512:101255>
MN Pullman ACMU 1100,<kuid:311512:1004>
MN P32ACDM,<kuid:126323:722>
MN SPV2000,<kuid:311512:1017>
MR F7A,<kuid:-1:100127>
MR F7B,<kuid:-1:100128>
M62-1675,<kuid:361619:44>
M62-1691,<kuid:432925:54>
NH FL9,<kuid:311512:1012>
NH P32ACDM,<kuid:126323:208>
NSWGR 44 Class,<kuid:-1:100812>
NSWGR 48 Class,<kuid:-1:100725>
NSW SRA 44 Class,<kuid:-1:100861>
NS Dash9 #8929,<kuid:95761:211>
NS Dash9 #9689,<kuid:95761:210>
NS Dash9 #9746,<kuid:95761:212>
NW RS11 339,<kuid:58422:100157>
NYCTA R46B Overhauled Subway car,<kuid2:58843:326:2>
NYCTA R46 Overhauled Subway car,<kuid2:58843:325:2>
NYC FL9,<kuid:311512:101299>
NYC F7A,<kuid:-1:100131>
NYC F7B,<kuid:-1:100132>
N&W Y6B,<kuid:523:1972911>
PCC-NonReal-101,<kuid2:82412:58199101:1>
PCC-NonReal-201,<kuid2:82412:58199201:1>
PCC-NonReal-301,<kuid2:82412:58199301:1>
PRR GG1,<kuid:-1:100841>
QR 2100 Class,<kuid:-1:100754>
RENFE 1800,<kuid:523:1051>
Rock Island FA1,<kuid:-1:100145>
RS3 - Norfolk & Western 307,<kuid:52779:307>
RZD CHME3-3172,<kuid:349860:323002>
RZD CHS4t-351,<kuid:354694:830351>
RZD CHS4t-519,<kuid:428217:18>
RZD CHS4t-543,<kuid:293699:22543>
RZD ER9-223 g,<kuid:293699:92223>
RZD ER9-223 m,<kuid:293699:922232>
RZD ER9-697 g,<kuid:293699:2697>
RZD ER9-697 m,<kuid:293699:26972>
RZD M62-1628,<kuid:151575:12>
RZD VL60k - 1222,<kuid2:164418:3322:1>
RZD VL80c-992/975 a,<kuid2:166294:75:1>
RZD VL80c-992/975 b,<kuid2:166294:76:1>
RZD VL80c-992/975 c,<kuid2:166294:77:1>
SAR 830 Class,<kuid:523:1057>
SAR 930 Class,<kuid:-1:100778>
SAR 930 Class single,<kuid:-1:100820>
sd40 2,<kuid:-10:192>
Silverton 48s,<kuid:-1:100734>
SNCF TGV SE,<kuid:-1:101412>
Southern F7A,<kuid:-1:100136>
Southern F7B,<kuid:-1:100137>
SP SD40T-2,<kuid2:45324:100141:1>
SP SD45,<kuid2:45324:100139:1>
Super Puma AS322 Helicopter 2,<kuid2:60238:9497:1>
UP Big Boy,<kuid:523:10070>
UP DD40X,<kuid:-1:100051>
UP GP60 #2024,<kuid2:113556:1000017:1>
UP SD40-2,<kuid:523:156564>
UZ CHS4-072,<kuid:293699:22072>
UZ CHS4-153,<kuid:428217:231>
UZ CHS4-189,<kuid:354694:922189>
UZ CHS8-001 a,<kuid:293699:8301004>
UZ CHS8-001 b,<kuid:293699:8301003>
UZ CHS8-014 a,<kuid:349860:128001>
UZ CHS8-014 b,<kuid:349860:128002>
UZ CHS8-023 a,<kuid:354694:8910023>
UZ CHS8-023 b,<kuid:354694:8920023>
UZ CHS8-076 a,<kuid:354694:8920031>
UZ CHS8-076 b,<kuid:354694:8920032>
UZ DR1A-821 g,<kuid:293699:2282>
VR S blue,<kuid:-1:100018>
V/Line S,<kuid:-1:100007>
1044,<kuid:-10:179>
2M62U-0026A,<kuid:361619:10026>
2M62U-0026B,<kuid:361619:20026>
2M62U-0030 A,<kuid:432925:107>
2M62U-0030 B,<kuid:432925:108>
Odd part is there are cabviews, bogies, and engine specs for SD70 built in, but no SD70s. Changing the search filter for "sd70" I get a few on the download station;
UP SD70ACe #8309,<kuid2:137823:590002:1>
UP SD70ACe #8485,<kuid2:137823:590001:1>
L SD70 Norfolk Southern PRR,<kuid2:86105:5498:1>
L SD70 Illinois Central Gulf AirC,<kuid2:86105:5494:1>
L SD70 Conrail Quality NS PRR,<kuid2:86105:5492:1>
None of those work "out of the box" in TS12, they all have missing dependencies and/or errors that would need to be repaired. How hard the repairs would be depends on how skilled you are with basic computer operation, there are tools and guides available and as long as you're comfortable with basic file and folder management they're pretty easy to learn and follow.