Lares rebuilds them

Lares Corporation Remanufactured steering gears (manual, power) cylinders, pumps, etc.
http://www.larescorp.com/index.html

Then and Now Automotive does, too.

Then and Now Automotive
447 Washington St
Weymouth, Ma 02188
Ph: 781.335.8860
Fax: 781.335.1925
https://www.thenandnowautomotive.com/auto-parts-store

Lares did a steering box for me 10+ years ago on a Ford truck. Excellent job. They'll either rebuild the one you send them or take yours in trade for a substantial core deposit ($150 back then) that you get back when they receive the core.

I think you have to go through a third party like Rock Auto or NAPA. I'd call them. Also call Then ands Now since their website is not very helpful.

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)