A 12mm can be found fairly easy, but that 19mm is going to take some huntin'. A good alternative is to take a 5/8" spark plug socket, flip it and put the extension on through the socket side, and the hex end on it will fit that 19mm hole. Since you're using that side just to hold it in place, while you're turning the other side with the 12mm hex, you shouldn't have any problems.
