I do not know of any military or surplus junk yards on Long Island or anywhere near by. There are a few truck junk yards that might has something in the back. I suggest the following:
D&D Used truck parts in bellport
Susquehanna truck parts in lindenhurst
Ive been to D&D before. Not a bad place. I would call before you go. Ive been told as Susquehanna having a ton of trucks. I have not made my way there yet but been told by other junk yards if your looking for trucks, that is the place to go. Also if you stop by a few places and say your looking for military stuff, leave your number. I was just passing by a place in brentwood and saw a deuce in the yard ready to be cut up. The yard manager let me steal a few things off before they took the torches to it.
If you find a place, definitely post up and let us know.