What kind of camo gear are you looking for?
You can buy those paint coveralls for pretty cheap, a few cans of camo color paint and make up your own.
Otherwise try Craigslist or local thrift stores. I know amazon, Ebay and many Halloween store sites have such costumes
but they'd be pricey for that many. Walmart usually carries camo stuff but end of hunting season is better for pricing.
Fabric stores, even WalMart's fabric section, usually has camo material. I like the idea of the camo tarp.
Craigslist or Freecycle are great resources. Ask for camo as well as military. Mention that you don't care about condition since it's for Halloween. You might get a lot of donations of ripped up stuff, easily fixed with duct tape (on the inside, LOL).
You might get hunter's gear, which is a different pattern, but it will probably work.
Post where you live. Someone might live close enough to you to help.