I'd also recommend wading through the files at the 3D Comics Collective (the link keeps popping in and out of the top 15). Some superhero costumes - especially the earliest ones - were pattered to some extent on military uniforms (such as the original (Shazam) Captain Marvel's), and some can be easily converted - and there is a good Warhammer 40,000 section if you're into high tech warfare. For historical gun-wielders, the site Leeroy5 named is one of the best, and Greylight Poser (another one that pops in and out of the top 15) has some good stuff in the Poser Archives (including duplicates of most of the WWII 3D stuff at the noxgeo site).