Needing a compatible replacement hub for vintage Hadco 394.

Might be that a front hub from an older car might fit if You can find one with a removable braking drum.
Other than that ebay is always worth snooping through.
Also, a local machine shop might be able to find something that would be compatible.
What is the matter with the old hub ?
If bearing race has spun in the hub then you might check into getting the inside of the hub where the bearing race resides knurled or machined out and a sleeve installed to bring it back to specs.
One time I was on a journey with a guy that had borrowed a trailer. After about a hundred miles we stopped for fuel. I checked the hubs for heating, YUP, one was hot.
got off to the side, removed the hub and the race had spun in the hub. Packed grease into the hub, shoved the race into the hub and packed its bearings.
All the rest of the trip that one hub ran cooler than the other three. LOL
True story.