I'd try any of the parts suppliers, I think the rear spindle was the same for decades.
Raber's, Baxter, british cycle supply, MAP, etc.
-Ben
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01 Bonneville, 56 Thunderbird, 68 TR6, 71 reversed head Bonnie (chopped), 79 HD Shovel, 67 MW Benelli 350 single, 46 BSA C11 plus many piles and projects.