Local rebuilder you can work directly with seems like the best route. That's gotta be a not very common thing!
I used to have a generator shop (yes, "generator", they'd been around that long!) I worked with whenever I needed alternator or starter stuff; they were by far the best. Dude even made a custom starter for me when I had a '54 Chevy that was converted to 12 volt but still had the 235 and 3-speed; he combined a few parts from what he had on hand and still gave me a great price on it. The original 6V starter had held up for a long time but all that double-time spinning finally had taken it out. Also once took him an alternator off a 9C1 Caprice that the nut had worked loose and let the fan/pulley wear out the shaft; instead of trying to sell me another alternator, he pressed on a fan/pulley from a Ford unit that had more shaft contact - sort of like those axle-saver wheel bearings. Man, I miss REAL shops like that...rapidly becoming ancient history.
Richard