Did you drill right through the frame Ted to remove the old rivets or just drilled out the head?
You can get the rivets through a Honda dealer. They are are blind screw type rivets with a corse thread, one hit with a hammer will knock them in via a pilot hole. The diameter though is very small and if you drilled right through the frame to remove the old rivets the new ones are very unlikely to fit. You could try getting a larger size as they are used for other applications.