There is a simple law of physics that causes the bronze to fail - its the fact that the two parts in contact are both bronze - similar metals. Putting a "dissimilar" metal between them eliminates the problem. It's the same reason they don't use a steel intermediate gear with a steel billet roller cam. They solved that problem using the bronze gear but apparently didn't consider the bushing it would be in contact with. Maybe they didn't count on rollers ever being used in high milage street use, who knows !!

As to the OP's question, you want a .030" thick Torrington washer. Obviously with a large enough hole for the shaft to fit through. You won't find the exact size because the shaft is an oddball .486 dia. but a washer with a 1/2" hole will work just fine. On some gears I've turned the underside down the thickness of the washer but I don't bother anymore.

Just keep in mind this fix only applies to the wear between the gear and bushing. If the gear teeth are chewed to crap you have other issues.