While the Fiero Store may maintain availability of rear calipers for a while, ( and they won't come cheap), eventually they will run out of them. IMO, it has become time to have an alternative bolt in solution. This may require adding a hydraulic eBrake but it can be done. The key will be to match new calipers that have the same capacity as the old.
[This message has been edited by Dennis LaGrua (edited 03-24-2020).]