Try these two businesses. Greenleaf shared them several years ago. Good luck. If we were such a green country then so many of the parts we need from time to time wouldn't be turned into scrap. We lost millions on the so-called "green" initiative "cash for clunkers". Just unmitigated waste!! Here are the phone numbers and businesses for odometer repair/parts, maybe.
Electric motor. The motor or the plastic teeth have gone bad. You can take it apart yourself and order parts or send it out to a repair facility.
Dick's Speedo/Tach
602-279-6463
Zepco Sales
800-527-4305