Side mirror mount replacement

Can anyone tell me the best way to remove the stainless steel side door mirror mounting brackets? I plan to drill out the stainless rivets, but they are not drilling out well dont want to grind and mess w/ the finish. also, where can I purchase OEM style rivets to remount brackets. I am painting my 378 Pete, and have to remove these, as there is corrosion between the mounts and door skin....wish I could afford to drop of a the local paint shop. thanks in Advance !!!!!