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They are so old now, I am not sure but a long time ago private owners chose no longer to fly these beautiful original P51 Mustangs ...

http://www.trade-a-plane.com/search?make=NORTH+AMERICAN&model=P-51+MUSTANG&s-type=aircraft

http://www.golfhotelwhiskey.com/want-to-buy-your-own-p-51-mustang-replica/

https://www.globalair.com/aircraft-for-sale/Mustang-P-51

http://www.tested.com/art/makers/558278-what-its-own-and-fly-p-51-mustang/

I doubt after so many decades the frames would still be serviceable and it would be terrible if another was lost to history due to an aerial accident or catastrophe . . .