Um, at an Airfix stockist? This http://www.airfix.com/north-american-mustang-iv-starter-set-1-72.html contains the new tool P-51D which has been around for a while now. Or you can buy it as a P-51D Red Tails kit for cheap as chips, and if that doesn't float your boat you can get it as a F-51D in Korean markings.