If you know anyone who has access to California's DMV records, such as someone in law enforcement, they can look up the VIN number in the Cal. system. It's a long shot... but you might also Google both your VIN number and the old Calif. license plate number. I have had some success in this "grasping at straws" technique.
You CAN request an ownership history detail from the Cal. DMV, but you need to prove a legal "need" to do so.
You might also post your VIN number here in your post. That way it becomes Google-searchable, and perhaps in the future a previous owner might find you as he's looking to see whatever happened with his old car