There's a line from the movie Operation Petticoat that goes "The boys in Vegas would say you're trying to make your point the hard way", and I think that often applies in cases like this. An owner has aspirations of restoring a car someday, and in most cases someday never happens due to a lack of time, money, illness/injury, spouse support, etc. And when said project car sits around untouched, it isn't long before throngs of potential buyers start turning up at the door inquiring if it's for sale. Are these folks serious hobbyists who want to restore the car like you want to, or are they opportunists who want to flip the car for money? There's really no way to tell. And when an owner refuses to sell, would-be buyers get frustrated.
My suggestion would be to approach this guy from a different direction. Instead of asking the guy if the car is for sale, or why he won't sell (like everyone else), ask him to talk to you about the car. He probably likes it as much as anyone, and people generally enjoy talking about things they like. A great example of this tactic is seen on that show American Pickers. They usually don't ask "how much is this?" right off the bat. They ask something like "what can you tell me about this?" and get the person to start talking about an item, which tends to lower defenses. Ask the Dad to tell you about the car, how he got it, why he got it, how long he's had it, what's he enjoyed the most about it, if he got lots of tickets, if he got lots of chicks, etc.
Then get him talking about his plans for the car. If he wants to restore it someday, suggest making someday now. Offer to help him find parts, references, resources, provide some free labor, etc. More often than not, guys like this just need a little motivation to get them going and once they get going one of two things happen: either the car gets restored or the restoration "dream" gets turned into a harsh reality with hard numbers and levels of effort replacing the fantasies of thinking about restoring a car and the owner becomes much more willing to sell. And even better, when they do make the decision to sell, they'll know you're someone with as much interest in the car as they have and be willing to work with you on a good deal.
