I was looking for a source for the visible rivets on the rear fenders of an AD truck and someone here had mentioned Big Flats Rivet Co. They had exactly the right ones Tubular 3/8" head x 3/16 shank x 1/4" long sold by the piece at $.10 each !. The shipping cost a lot more than the rivets.
I replaced mine with screws. I simply took round head screws (#10 as I remember) and put a couple nuts on them, and put it in the vice. I then polished off the head using a da sander. Worked like a charm 20 years ago and still look good.
1948 Chevy Pickup Chopped and sectioned owned since 1974 when I was 15.