Most "surplus" now is cheap repro. I am a military collector, as well as a gun enthusiast. The original stuff can still be found in plentiful numbers, but it is mostly modern stuff, not much nam or soviet stuff. I noticed there is a lot of Czech, Yugo, Romanian, and some Russian stuff out there now. The only problem with the original gear is that the prices are high, which is why many stores turn to repros and cheap stuff.
In terms of surplus, a lot of people buy paracord, BDU uniforms, helmets, and ammo collectibles.