Tleve,
I commend you for trying. But, what you are asking is, though good for it's purpose, going to be a very hard sell as you have already found. As one who makes 18th century clothing for museums and reenactors, I can give you a couple of reasons as to why you are having such trouble:
1- Most folks don't have 2 or 3 outfits and we are now in the begining of the start of the reenactmen season. So, folks might not want to lend things out if they need them for an event.
2- The fear of the unknown: By this I mean the person's equipment. As one who has done films and the like, film companies always want to "borrow" things for their shots. Problem is, the equipment is often ruined or severly damaged. Not to say you would do this at all given the purpose of your show but the thought still lingers in folks's minds.
3- Unlike some other periods of reenacting, there is no real "reenactor stor for the native american" All of the items are hand made, and at least with my equipment, I have to spend days worth of time in the woods collecting materials just to make a piece. Therefore, much of the equipment is irreplacable and often extreemly expensive.
I do wish you the best of luck with your project though. A suggestion might be to line some folks up to show up to the event with their clothing on themselves. This will ease the inhibitions mentioned above and will also serve to show your "clients" how the equipment/clothing is worn properly.
I hope this helps.
Joshua