[rotorwrench]

A person needs a source. We lost Big Flats Rivet Co not long ago. Now you have to check 3rd Gen Automotive to see what they have. Frame rivets and some 3/16 body rivets are available but your in a different territory with the countersunk types. Hanson has a selection of steel rivets but I don't know what degree of countersink types they have. Aviation uses 100 degree but others may be 80 or 90 degree. They also have flat head and brazier head.

Common sizes are 1/8, 5/32, 3/16, and 1/4-inch sizes. I'm not sure about 7/32. Rivets expand a fair amount when driven or squeezed so the holes end up oversized even when a person is careful removing them. Countersink rivets in thin sheet metal make the countersunk side hole too big for easy driving. FORD used brazer head types for body rivets but I don't know about the body subcontractors like Briggs and Murray. They likely sourced their own fasteners for the most part.