There is a military and civillian version of the AN/PVS-14 although it isn't what you might think. Military pvs-14s are always adjstable gain and typicaly have nicer tubes (due to contract specs, but not always, some civi systems have damn nice tubes). Oh, and they are marked "US property" on the housing. That being said, you can buy a PVS-14 that is exactly the same as the military versions in preformace. Finding a unit with adjustable gain and a nice tube is not too hard. Even finding a housing with "US property" on it can be done, although I would NOT recommend it. All PVS-14 accesories that fit a Military PVS-14 will fit a civiy one. Even the head mount. The only differance I can think about is in the headmounts. Both look the same but the military mount is wired so that when you remove the unit from the face mask or flip up your helmet mount it turns off. You can use this adapter on your civiy unit, but unless the body has the connections for it it won't work. You can find a good unit here on Equipment exchange or at www.usnightvision.com. I am shopping for a unit as well, once I get the money together....
D vs Regular 14, D will have a nicer tube, omni 4 or 5 at least. There is also a AN/PVS-14A, which is a PVS 14 with a few improvements, 1. takes one AA batt. 2. redesigned lanyard ring, and that's all I rememeber off the top of my head.
Good luck,
mrf2