Tamiya's German Grey looks like a good bet and I'm not quibbling with Jentz and Doyle. The problem is that "grey/gray" (they can't even decide how to spell it) is a very odd color. Folks with no taste for color mixing would make a grey by mixing white and black. I'm not sure what would work industrially, but that might not necessarily be the best way to do it. If you wanted a really deep black pitch to mix with a white paste and some thinning agent, you might well have a kind of "chromatic black" which is made with blue. Indeed, there's no doubt that Tamiya "German Grey" has a bluish tinge. BTW: the many photos of Panzergrau vehicles in Greenland's book are all "dark grey" but with a very subtle bit of blue. He used Hannants enamels but recommended Blue and Dark Grey for a Tamiya mix - I'm sure German Grey wasn't available when he wrote. It's true that I've seen some models that have their kits a kind of greyish blue and don't doubt that it may be pretty but is not history. This issue has precedent. I do believe that American sailors throughout WWII were given a kind of deep purple paste with a big bunch of white paste: depending on the ratio you made haze grey, deck blue, navy blue.
Do appreciate the thumbs up on Tamiya. I have a couple of bottles so I won't go looking for more. Can also use it as a benchmark to whip up a batch of Panzergrau with acrylics when I run out.
Eric