Buying new rivets worked well in the early 70's in SoCal with all the Aerospace activity. Thursday morning at Fullerton Air Parts (Aircraft Spruce at that time was "down the street, dealt only with wood and was by appointment only) got you rivets that would drive at 60 psi or so, raising to 80 psi by Saturday.
I had access to "professional" HT ovens, analog controlled, and following the above procedure, gave you rivets that drove at 40 psi, barely "tickling" the rivet gun trigger, "plop, plop, plop, plop" If you kept them on dry ice, the pressure requirements increased more slowly, but eventually got to 80 psi or more after a few days. Soft rivets drive with minimal, if any, distortion of the surrounding sheet metal as the clinch pressure was less or equal to the "stretch" resistance of the skins you were riveting.
935 deg F, yes, but you need a digital controller now. The old analog controllers were +/- 10 deg and you risked exceeding 938 deg, which scrapped the rivets.
Also, only anneal clear anodized rivets. Annealing colored rivets is a chemical no-no.
Onward and upward