In NY the dmv has a form you can fill out for lost paper work on boats and skis. You have to take pictures of the ski and pencil trace the VIN tag for them. They'll give you a NONtransferable registration and new regi numbers on the spot until the paperwork clears at the capital. It takes a few months, but if all goes well they'll send you transferable tags.
I was able to register one of my skis this way that hadn't been registered 16 years and there was no possible way of getting information from the previous owners.
Kind in mind they need a VERY GOOD explanation why theres no way to get information from the previous owner.