Have you tried ebay?
I've seen WWII German a/c stuff on there and it can get pricey!
My dad has a small chunk of a Ford tri motor skin that we helped restore and at the time i never thought to keep any of it but i could of had some skin from a P51 and a B25 that i did some restroration work on for kermit weeks he use to have his museum in so. miami and then he moved it to polk city near orlando.
If you ever want to take some vacation time and volunteer you can they are allways looking for free labor if you know anything about aircraft maintenance you'll get to do some cool stuff there.
http://www.fantasyofflight.com