Hi Amtrak,
The DLS, of course, has some Espee equipment. In addition to making the obvious searches, If you search for "Harriman" you will find an extensive line of cars of Harriman design created by Bendorsey that can be lettered for any road of your choice. If you search for "TOTC" you will find an excellent set of wooden cars he did as well, that can be lettered for Espee or GN. I know they worked fine in TRS2006 and TS2010 compatibility. Have not tried them in TS12. If you don't mind payware, Paulz Trainz has a very good set of Harrimans in several different liveries. Can't help you with Great Northern, sorry.
Bernie
PS: Almost forgot, well, I actually forgot :hehe:, that you can find some excellent Alco PAs at the RR Mods website. They are freeware.
B