We have a couple of antique malls here that often have some good finds. Especially when they do their big parking lot sales a couple of times a year. i have found many a wanted kit, and the vendors are usually willing to haggle.
A local RC club used to do a swap meet every fall. RC stuff, diecast, and plastic. I always found stuff there, for excellent prices, but they haven;t done it for a couple of years.