Take a picture of it along with belt/pully measurements and then go to your local pick-a-part salvage yard and start looking at the small foreign cars for something that looks similar to what you have in the Kubota. I have a BX23S and have never had a need for more amperage to keep my battery properly charged. I contemplated adding a connection to the battery terminals for an external battery maintainer since I don't use my tractor very often, and it can go for 2 or 3 months without starting. When I need it, the battery is always charged and starts the tractor. On my old BX22 which had the same type of treatment of use, the original battery lasted 11 years before I had to replace it.
