If you want something a little less common, look into one of the vests the IDF (Israeli Defence Forces) designed. Mind you they're not cheap, but they're built tough and the designs have a LOT of operator input in them. I bought an IDF Recon vest a while back - the manufacturer was Archidatex - and I'm very happy with it.
Couple things about these vests, though. They ain't cheap. Mine came to a tad over $200.-, but it's worth every penny, IMO. The big ones, like the Recon or Medic versions are bulky, and have a LOT of pockets, some of which you may not need. I ended up pulling the integrated backpack off mine, because it simply got in the way. You also generally won't find them with back pockets for a camelback, though I wear mine over a low-profile carrier and it works. Lastly, the vast majority of IDF vests are OD green, which may or may not be to your liking.
If you're interested, let me know. The site that azsarge linked to,
http://www.practicaltactical.net , has four versions for sale. Other sites also have them. I've read and heard about non-Israeli troops using them on an individual basis, so it won't neccessarily spoil your costume if you're wanting to look like a U.S. operator.
-Chris