CAPTPG

I have an early 302 Z28 12 3/4 inch flywheel and bell housing. Am having trouble finding the correct starter drive end housing to fit the bell housing opening. I've been to the local rebuilder and tried their assortment of housings, but haven't found one that fits. Didn't realize that it was such a rare animal, or is it? Maybe I'm just looking in the wrong place. Any help would be appreciated.
Capt PG