Hi blausser! Welcome to the board.
Courtesy Aircraft has a good P-51 project for sale.
http://www.courtesyaircraft.com/N51JY%2 ... 0Specs.htm
Like cvairwerks said, It is a very expensive proposition. The least expensive P51 project I've seen was the few remains of a firey crash, and it was still pushing 100k.
The chances of you finding an unclaimed P51 anywhere, well, they are pretty slim. If you do happen to find something like that on the planet, it will cost you more than the project listed above just retreiving it.
If you're rich and can take a few years off of work, you're gonna have a good time and come out with a Mustang.
If not, I recommend starting with a different bird. Restore it, and move up to something bigger. Do that a few times, and in 20 years, you might have what you want. Thats what I am doing.
On another note, operating almost any warbird is very expensive, very, very, expensive. Especially P51's, Bearcats, Corsairs, Ect. I've heard that a P51 just sitting in the hangar is going to suck up 40-50k a year.
Good luck on your search! You have come to the right place. If anyone has a clue to where the kind of bird is that you want, they definately post here.