rivet setters are easy to make from the back end of an appropriate-sized drill bit. heat till brite red, let cool slowly. then carve/form the depression in the end. for soft rivets, re hardening would not likely have to even be done. round diamond burs can do a pretty neat job of carving out the dome shape needed.
sorry-- i forgot to mention how very nice this piece looks. fascinating to behold. color, texture, engraving. cool stuff.