A friend of mine purchased an old commercial bldg that had a circa 1900 tin ceiling. He was able to work a trade with restoration contractor who removed the tin ceiling and installed a new lower ceiling complete- framing, drywall,finish, lighting fixtures, wiring, ductwork, all at no $charge in exchange for the removed tin. I know that all old ceilings aren't going to be that valuable, but it makes me think that your old copper ceiling is sure worth asking around. Most larger cities have architectural salvage businesses, try the yellow pages. Also restoration specialists, trade mags like Old House Journal, maybe eBay? do a Google search.