Some burros were sold as kits and I don't believe came with vin s. I have never been able to locate my vin even with the frame removed and careful examination .l just made my own vin and home built ownership.
Vin number should be on the outside and/or the inside of the towing tongue. I had a 1980 Burro and that's where I found it. You may need to sand off some rust to read it.