I was speaking with Aerodonamic today and he suggested we put this on our forum, so here goes.
Don was looking for the in-dash AC evaporator core for a Fiero and he started with Advance. They couldn't get it. Neither could AutoZone or O'Rielly's auto parts stores. It isn't available. I've checked with AC/Delco and they don't list it. This is for the 85-88 model years. The 84 is different and we didn't check availability for that year. The AC/Delco store first looked for the condenser in front of the radiator and told me it wasn't available either.
The Fiero Factory has used ones and The Fiero Store has a limited number of new aftermarket evaporator cores. They are first come, first served, so there probably will be no more once they're sold.
It might be advisable to grab one from the parts yards to have just-in-case.