Since there hasn't been a response with Dan Zellman's comments, I'll add what I know. The Syncron AU7/AU7A aka Fairchild F22 were made by Syncron in Wallingford, Connecticut. They also made the S10 cardioid, which is the subject of an article in the Journal of the AES. I've seen two versions of the AU7 capsule; one looks like a CK12 but with only the front diaphragm connected, the other uses half a CK12 capsule with a perforated plate replacing the other half. In each case I've seen, the diaphragm is 25 micron polyester, 3 to 4x as thick as it should be, with predictable results.
Jeff's information on the 21 volt mercury batteries is right -- they are no longer available. The circuit is very simple and adapting it to 48 volt phantom is not difficult. But Jeff, would you post the original link to Doc Cavalier's interview? tinyurl links go away, just like ebay ones do, and this one is 404.
The connector seems to be a homemade hybrid using small Tuchel/DIN threads and an Amphenol multi-pin insert. The Amphenol types are still available from WPI (
www.wpi-interconnecto.com) but the threaded ring and cable clamp seems not to be.
At some point the wireless microphone maker Vega, in Santa Clara, California began selling the Stanford-Omega omni and the S10 cardioid as Vega/Syncron mics, but the AU7 was available only from Fairchild. If someone has more information on this, it would be good to know (Klaus, you don't need an archivist, it happens here automagically, as long as people don't post tinyurl's!)