First you need to know how many wires are needed? I believe most are three wire, but could easily be wrong. Most motorcycles, snowmobiles, and PWC's will use the same type and can probably be utilized. I used one from a Kawasaki motorcycle bought off of Ebay for a killer deal. If I remember correctly it was under $20. Search Ebay for a motorcycle regulator. Typically you can buy a universal regulator for around $75 US. I just had to cut the wiring ends off and find a place to bolt it on. They get very warm/hot depending on how much energy it is producing. It will also need to clear the motor cover.
Either way go and look at your motor to see what it needs, then report back. Some motors even come with the regulator installed.
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You can see my regulator on the left with the cooling fins. the yellow wires are from the stator. (Picture was actually taken to show my awesome on water repair of the broken link that changes timing