Matt,
The rivets are size 4-6 and are available from Aircraft Spruce(06-02300)  for 3 cents a piece.  I've ordered pads from several different sources over the years and can't remember what rivets came in the relining kit from Lancair. Seems to me they would know which size to send.   I know the rivets that come along with reline kits from ACS are too short.  Once I discovered that Matco brakes use the longer rivets, I ordered 100.
Chris Zavatson