A couple of years ago I got some replacement DX7 keys from oaktreevillage.com phone 719-964-7205
He might have Korg parts if he's still doing it. I remember way back a Yamaha repairman telling me that the Korg M1 and the Yamaha DX7 both used the same keyboard from another manufacturer and that the keys weren't similar, the were identical.
I've got a few keys for my M-Audio keyboard from M-Audio directly and ended up buying a broken keyboard for parts 'cause it was cheaper.