I agree that this is not an unusual failure over time. While the bolt is not special except for maybe the length, the locking washer is somewhat unique. One tab bends down into the housing and the other tab is bent up to hold the hex of the bolt.
I would check to make sure that the threads in the housing are usable.
I would say they are both special bolts as they would be hard to find. The part numbers have been superseded many times and the ones shown don't match my 32 catalog or my 34 catalog and the catalogs don't match.
I would think finding them locally would be best but if you can't send me a private message.
I'll add that they seem to be hardened. I only know this since both in my starter have broken. I suspect that the previous owner used regular bolts that were cut down and were likely not hard (strong) enough. Both times required a trip to the machine shop to have the bolts drilled out of the shaft.
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One of the bolts has a pin on the end to lock it onto the shaft. I think that was the end coming from the armature. Both bolts have a somewhat special retainer and a low profile head. A friend had two of the jars that had all the different bendix bolts. When my starter bendix bolts broke he gave me a set. They are still working on the starter. Originally the bolts were zinc coated.