The Avex rivets you want are:
1661-0410 or 1691-0410. Both are identicle rivets but the 1691-0410 has a different (gold tone) nail. I use both depending on what is available at the time.
Aircraft Spruce only sell the 1601-0410 rivet which has the smaller head that happens to be perfect for the installation of the Trailing Edge modification if you choose to do that mod, but does not have the standard head you want for everywhere else on the Lazair. So I'd suggest sticking with the two numbers at the top of this post and you will get the right rivet. They are considered low-profile headed Avex Rivets and match the best ones Ultraflight used...and the ones Chappy described above.
George Curtis