Each of these:
BI Grain,<kuid2:30671:27205:1>
BI2 Grain,<kuid2:30671:27220:1>
PL Grain,<kuid2:30671:27370:1>
can produce flour. Place one of them beside one of the flour mills such as:
Alton Flour Mill,<kuid:58223:27156>
Flour Mill 1,<kuid:61119:28197>
and you'll have what you want.
Bob