Just a few thoughts
There is a huge collection of military maunals in Tooel Utah -
http://www.armyjeeps.net/Tomlin/Toml...ollection.htm- scroll all the way to the bottom
from the site "This is 1,500 linear feet of manuals on 50 plus shelves, weight about 20 Tons. There are 30,000 plus, one each documents. The Library includes very comprehensive collections of TM's, FM's, TB's, SNL's, TB Ord's, FSMWO's, Etc."
So I think it quite possible to PC to find FM or TM in alot places in US.
also I think that many guard units might have nessary techs already
State Guard: What did you in the Army/Marines
Tech: I was a tank mechainc from 68-72
State Guard: Great we job for your welcome broad Sgt Major
Tech: When I left I was only a Sgt
State Guard: Well your a Sgt Major now, Next
Lastly I don't it too much of stretch for the PC to find an old AFV/APC in Texas/CA/NM. The many could have hidden away or it by passed cause nobody knew what do with it or did want it headache of trying to figure how they were going to maintain it fuel ect.