It is also possible to make your own from a piece of steel rod that matches the diameter of the hole. Just cut them to length (I try to keep them about 3/16" or 5 mm long) and then rive them over with a ball peen hammer. Use the flat face of the hammer when you are done to put the finishing touch on them. The steel rod they sell in most farm, fleet, and big box stores works just fine.
Mark