Help me find my great grandpa's truck

[monocogger]

tl;dr

I sold my pickup to a guy in California. He flew to WI and drove it back. Fast forward 11 years and I want it back. I have the vin number and two previous license plate numbers. I talked to the guy I sold it to and the guy he sold it to but that's as far as I've been able to take it. I need some ideas.

Full story:

When I was 10... 23 years ago, my great grandpa told me he would will me his 1971 GMC 2500. He bought it new, waxed it weekly and drove it rarely. A year or so later he passed away and being that I was too young to drive my dad used the truck for a year before he parked it behind our house where it sat in the elements for 8 years. One day I came home from college and saw it sitting there and I decided to claim my inheritance. It had not been touched in 8 years but I raised the hood hooked up the jumper cables and gave it a spray of ether. I turned the key and it started like it had been run earlier that day. I drove it for a few months and then decided I needed the money for my upcoming wedding more than I needed an old gas guzzler. So I put the truck on Cars dot com and a couple months later a gentleman from CA agreed to buy it from me. So I picked him up from the airport, took him to my parents place where the truck was being kept at the time and I wished him well on his journey back to CA. He drove it up and over the Rockies without too much issue. Now that I'm older, I can appreciate what I had a lot more. I have a young son who LOVES old trucks. I'd love to find my family's truck and bring it home. I've contacted the gentleman I sold it to and he gave me the VIN, as well as the contact info of the guy he sold it to. I contacted him and he said he no longer had it and didn't have any information about the new owner except that he sees it driving around Ventura, CA every once and a while. I'm not sure what the CA DMV is willing to provide me or how much it will cost. I'm hoping one of you will be able to help me out. Thanks in advance.