Brewers has one listed on their site:
Product ID: BH859
BH859 SMALL BLOCK 10.5" BELLHOUSING, 75-80 A/F-BODY/1976-80 TRUCK OVERDRIVE, RECONDITIONED
Details
Reconditioned original 10.5" small block bellhousing cast #3743859 to fit 1975-6 A-body/1975-80 F-body/1976-80 truck (can also be used in...