The 38mm pistons calipers were also used on rear of Fiat 125s, and possibly others too, so maybe expand your search criteria beyond the Monte Carlo and Scorpion.
Repair shops unfamiliar with those calipers as being different from the more common Fiat 124s and X1/9s were known to simply replace them with generic rebuilt calipers from parts suppliers, since they are interchangeable from an installation standpoint. I once bought a rebuilt rear caliper for a Fiat 124 and received one with a 38mm piston, showing that the cores returned from Scorpions make their way through the same system of parts rebuilding.