Been waiting for someone to organize something like this, a 3D library. Anyway, I'm not entirely sure on the limitations of Unity, so each weapon is about 2000 polys when triangulated. Here they are:
1) Jungle Primitive: Download
2) USMC Ka-Bar Knife: Download
3) Musashi No Shana Katana: Download
Credit would be nice, too, if you plan to use or reverse-engineer them in your Unity projects.