Unfortunately, there isn't much in the way of free military clothing for Poser. PoserWorld has the most uniforms and stuff, but most of them are British, not American. There are also a few historical (WWII) uniforms for M1 and Dork. For modern clothing, we're pretty much out of luck.

I did pick up the Desert Storm uniform from DAZ. With the PC 50% anniversary discount and another 25% off as part of the David and Stephanie Petite sale, it was only $7.

Maybe some of the Poserworld uniforms could be re-textured to be American military uniforms?