Thanks Freddy,
I have two rivets, a cheap generic eBay one that actually has screws, and a new one that came with my vintage milgauss.
Since I posted the above, I took my new unsized one to a nearby jeweler and he had the rivets to do it.
I won't get it back for a week but he's done work for me before and is very good.
As for the single MBW rivet bracelet that I handled...I agree with you.
ETA: The jeweler told me the rivets are the same ones he uses for watch bracelet clasps..so
he was very familar with the operation..he showed me an assortment in a box he had.