Maybe you can clear something up for me. Why can't marine figures be used? Except for the different fatigue hat, didn't they wear the same types of fatigues? I was in the Air Force in the 70s and 80s and I think we wore the same type of Stateside fatigues. Granted I didn't pay that much attention to them but I know we had the same jungle fatigues. We had cammoflaged and our tiger stripe fatigues were variable according to which local shop made them for us.
I have a few Tamiya and Academy figures left over from their M-113 kits and maybe a couple others. if you think they might work.
What part of the world do you need them to represent, S.E.A. or Stateside/Europe?