A Pdf from the Dovo site states that they are "German silver" which is an alternate name for nickel silver (generally 60% copper, 20% nickel and 20% zinc). They're far harder than the nickel-silver rods we get from the knife-making places, so I suspect there are several different formulations running around calling themselves "nickel silver" and they've got one that makes extremely hard rivets.

I get mine from the Invisible Edge in the UK. To make the shipping more economical, I generally add a razor or two to the order. Make sense, right? Not like I have a razor addiction or anything.