I assume you have a solenoid equipped starter?
Any '55-62 235/261 starter with solenoid from a stick or powerglide car/truck will work. '55-59 GMC 6cyl will work also (with solenoid start).
Starters from a hydromatic equipped vehicle will require swapping the nose piece.
Used ones show up on Ebay all the time. You can get most of the internal parts new from the usual sources. Rebuilding it yourself isn't difficult if you have the parts.