well, if you are looking for an indoor range where you can rent firearms and buy ammo, i suggest you look in the phone book/yellow pages under "guns" or "shooting".
if you are looking for empty .45acp brass, they may have some for sale at a range, or you can try a store like cabellas that sells reloading and shooting equipment.
you can skip looking for anything in key west, i go there every year.
enjoy your visit to the U.S.!