If the vessel was of US registry, and if the vessel was documented, and if the vessel is still documented, you might start online with the USCG National Documentation
Center website. There are lists with limited information about documented vessels on this site. If you really want to find the boat, and it meets the above criterium, you can pay to have a title search done. Or... You could call the last marina the boat was in before it was sold, and see if they have any information. I would say, that unless the boat is something really unique (not just to you), at 30+ years old, you may not want to find her. Other people's idea of mantaining a vessel may be a dissapointment to you.