Butch Schroeder of Danville, Illinios has a super restored P-47. He is a real stickler for originality and researches the colors quite extensively for his airplanes. He is also the owner of the fabulously restored F-6D of which some of you may be familiar.
Possibly a contact with him could give some insight to the proper color, and how it was replicated.
Another super stickler restoration facility is Yanks Air Museum in Chino, CA. They have a P-47D, and the YP-47M used in two aborted attempts at competing in the post war Bendix Race (it's assymetric Curtiss Electric paddle blade prop, now fitted, is really something to see in person). These ships are on display, and the museum could be contacted by commercial means.
Lonestar Flight Museum puts out some beautifully operational restorations, however the airplanes are subject to some artistic license. Personally, I liked the chrome on their Tigercat! My personal contacts at the POF museum wouldn't help with this as their stuff is painted from the Sherwin Williams catalog. But, who is to say their PRU Blue Spitfire is the wrong color, right?
Have fun,
Chris...