I recommend ebay too. I bougth my m-tec 68030 board on it. OK, this is the slowest 68030 turbo card made for the a500 i think. It's only 14MHz, and you can overclock the fpu only, but compared to a plain a500 it is lightyears before it.
However the gvp cards has it own backwards too, they only work for its own gvp memory modules. So beware, you buy only with memory, else i think you will never find any of these modules.