Yep it's a Milspec, made generally by Cannon or Bendix (some by Amphenol) for military and aviation use mostly. As mentioned a more commonplace connector might be a better option but it has to meet your voltage and current requirements.If it's a Mil connector, it should have a part number on the flange or the barrel.
This 3 pin flange mount is actually the same one that I ordered as a replacement, but I ordered it from Amazon. I'll share pictures when I have it all together. Thanks!
There are rubber seals on all the connectors and panels of the computer. This makes sense as to keep it waterproof since the specs claim the computer can be "hosed down". I don't think I'm going to ever try that.From what I understand they are used for boats as well as harsh enviroments that cause the metal to rust easily, or enviroments that have excessive vibration.