About 10 to 12 years ago, before the introduction of the Snyder & Short series of paint chips and the subsequent White Ensign paint line, Jon Warneke of Iron Shipwright wrote an article for SteelNavy. He used the 1929 Munsell color codes called out in the specifications and paint chips from his local Dutch Boy paint store to come up with a set of close-enough-is-good-enough color matches for Royal Navy and US Navy World War II paints.
On this page you will see his opinion of a close color match to USN WWII Navy Blue (5-N). If you can't find the color locally and choose to not order from White Ensign, mix to that and call it good.
http://www.steelnavy.com/usnchips.htm