Just a story about researching the history of my first pro car - the '67 S&S high top - I purchased it in '08 from a salvage yard on Long Island, NY - who could provide no history what-so-ever. The only thing I had to go on was the name on the roof - Billings Ambulance Service - which I assumed was someone's last name. (The S&S builders tag, showing who the car was built for was long gone - although, at the time, I didn't know it should have one.) On the trip home with the car, I was talking to a friend, who wanted to know where the car served. When I said the name, she immediately made the connection to Billings, Montana - which I felt was unlikely, with the fact that the car came out of a salvage yard on Long Island. However, upon getting home, I realized the keys were on a plastic key chain, advertising the "First Citizens Bank of Billings, MT." I tried doing as much research as I could - scoured the internet, emailed several museums in Billings, but could find no information on Billings Ambulance Service. Finally, after two years, I took a week of vacation, hopped on a plane and flew to Billings. I started with the fire department, as I figured someone there would know, which led me to the current ambulance provider, which led to the previous owner of Billings Ambulance (and my car.) I came home with a stack of photos of my car in service, lots of great stories, and a new good friend.
Moral of the story, persistence pays off (sometimes), it's harder to be told no in person, and if you can't find the previous owner, look for someone who would have interacted with the car - maybe try the local fire departments - they probably would have worked accident scenes with the car, and may be able to point you in a good direction.