Jay-Cee Rivets, they have all the information you need on their web site, including how to order the correct length and the proper head sets to upset the rivet

http://www.rivetsinstock.com/

It can be a pretty costly investment for the couple rivets you'll need. Bags of 100 are usually about $7 but shipping on that bag will drive you over the $15 range. Head sets are about $30 each. Try to get everything you need on one order and make it one shipping charge.

That said, you'll never predict all the various lengths and diameters.