old airplanes?
not to be smart-aleck Mark, but airports? Marine repair shops?
ours has a place that fixes floats.....lots of them are pulled apart, so scrap bins full of stringers and skins etc. Not a huge variety of stuff, but free, or a case of beer gets all you want!
Another outfit used to rebuild Islanders....so a TON of strange but wonderful ( to air-geeks) parts and pieces end up in their dumpster.
Funny, but quite a few parts have ended up on my old lawnmower etc.....but I am preachin' to the choir aren't I!?