I found a link for model train repair from a seller who had various custom tools for sale for riveting like this. He had made custom 'anvils' to fit specific applications and also offered a spring loaded center punch with modified tips to fit the rivets.
I had one with a ruined tip. I had a machinist at work face off the tip then drill a 1/16" hole a few tens of thousandths of an inch deep.
I found many other sizes of brass rod & tube from K&S Engineering/Metals, a hobby supplier. They offer most of this material in a 'cut to length' service in the US and Canada, not sure if elsewhere.
I need to find out if I can special order small length of a couple sizes closer to what I need from them or from a local dealer.
For a mandrel or anvil (not sure of correct term), I plan to use a cheap set of 'nail sets' which look like punches with countersunk tips, held in a vise.
What I need to replace is not extremely critical. Two rivets are for a pivoting film spool shell and don't need to be (cannot be, actually) brute-force-tight like rivets for foldign arms, doors, etc. and the other piece was a stepped rivet that the shutter release linkage slides on. I may be able to make something from a piece of rod & tube & epoxy it in.
I'm wrestling with figuring out checking focus with ground glass and getting the center lens cells loose to clean.
I hope to finish the rivet mess soon.