Answering my own question here... The connector was made by a manufacturer called Pressac that back in the day would also make CRT sockets, etc. They're still on the market but only make network cabling and such...
Bottom line, that connector is no longer made or carried by anyone so you can't make your own extensions. This also explains why Sambers switched to Lumberg connectors for the newer Hantarex monitors (post 1993).