I went to home depot (and lowes) today and found that they don't sell rivets by 6-8 or 6-10 designations. They are 1/2", 1/4" etc, with nothing longer than 1/2". Of course, the sales guy couldn't tell me how to translate those sizes, but I did find an explanation on someone's ebay site. I also noticed that the part numbers on the box refers to the rivets by those numbers (even though the sales guy said they didn't.
Where else would sell the longer rivet lengths I need? I did buy a box of the 6-8's, and we have a box of the 6-10s (part of the rivet gun gift). But neither of the two stores sell longer than 6-10s.