Okay, so maybe I'm just a lucky guy, and they really are impossible to get, but I am not having an enormously difficult time finding a 5167A at a dealer. I casually expressed interest in one about a month ago, and my AD just called me. On top of that, I've found several more at ADs outside of my area, willing to ship via a 3rd party or themselves. In my experience so far, the 5167A is certainly not in every dealer, but it's not exactly a difficult get, either. To put it in Rolex scarcity terms (which everybody knows), it appears to be as difficult to find as a Rolex Explorer II... A little easier than a Sub, and nothing like a Hulk, Daytona or Pepsi.
So why on earth is the grey market pricing what it is? Close to $40k for used examples? People trotting out the old 35mm versions that nobody wants for north of $22k? Who are the people buying grey market Aquanauts for this money? Clearly enough to support the current market pricing, but I can't imagine anyone is having that much more difficulty than me sourcing a new one from an AD (for less than half the current grey market pricing for used)... I mean, I'm a charming guy and all, but nobody's that charming, ha ha.
So what gives?