When I purchased my SRX600, I didn’t realize it is next to impossible to register an old vehicle without the previous owner’s title or registration. After much searching and querying, I discovered a technique that works in Massachusetts and many other states. First register the vehicle in Vermont, and then use the Vermont registration to register the vehicle in your home state.
It is perfectly above board to register a vehicle in Vermont even though you don’t live there. I suppose Vermont just wants the sales tax revenue.
Here’s the website that I first learned about this technique.
Here’s another write-up of the technique from the advrider.com forums.