I have the entire seat (back and bottom). I'm replacing the springs in my front buckets, and I just assumed that the rear springs would be toasted after 40 + years.

Another thought was that I didn't want to spend all the time and money recovering the rear seat and then end up with one or more broken springs. Sort of a "while I'm at it" thing.

Both NPD and Ames do not have rear spring sets AFAIK.