McMaster Carr (onolne shop) has
steel solid rivets. They sell in large quantities but are relatively cheap. I recall riveting sheet metal in my dad's shop. He used just a few sizes and used a
rivet set for use with a hammer. The rivet was put in the hole in the metal to be fastened, bucked (backed up)with a heavy piece of steel, hit once with the set to upset it, then the set was moved to put the rivet into the hole in the set and hit again to push the two pieces of metal together, then back to the heading portion and hit a few times to form a head on it.
FWIW, the original rivets holding the rear fender crown brace to the fender were steel tubular style, but finding tubular rivets short enough and with the low domed head to match the originals is tough to do.
I'm pretty sure it's spelled "despot".
