I am about to teach a class on rc building. I would like to buy crashed airplane parts to use to build test items for things like wing components; aileron's, flaps, rudder's. I would also like to buy a crashed plane that had retracts to use as a learning tool to show how to build and operate. Also engine test stands along with a lot of other stuff

A swap meet would be a good place to find things like that. Some times you can find some good stuff out there. And other times you will find a lot of glue bombs, planes that been around for years with a lot of necessary glue joints reinforcements.
Or Build a kit from plans up and bring in the parts already together but unfinished with components so you could install. Would make for a clean work area on the plane itself.