The drives that would fit are very rare and hard to find. You might have to actually buy another whole A500 to salvage the drive from it. You can get other PC drives that are modded to work, but you would have to hack the A500 case to get it to fit.
Has the buyer tried to see if the eject button can be fixed? I as able to glue mine back on and it was very secure and worked great. It's just a plastic piece that clips on.
