Rock Auto lists the gasket

https://www.rockauto.com/en/catalog/chevrolet,1957,bel+air,3.8l+235cid+l6,1326147,cooling+system,water+pump+gasket,2148

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)