The Athearn rep is correct! Still, it's the only car in N scale of this type.
It's funny. I was recently looking at how to make the exact car type CSXTer linked to in his post. The waffles are OK and the roof is fine, but every car I've come across has six ribs not five, and the ends should look like PS-1 ends (the CSX cars were rebuilt).
After I posted I did some digging and there were more releases than I thought, but not much more ( I was counting releases not road numbers). So far I've found:
Atlas Trainman boxcar
Atlas 60' auto parts car
Atlas FGE car
Fox V PS 5344 Cuft boxcar
Fox V "Soo Line" car
Athearn 50' Berwick car
Intermountain something or other car