It's about 6mm in diameter. Anyone know what type of socket that is or where to source one?

Backstory:
I just purchased a used (barely) Flytec 4010 variometer (for paragliding), and would like to be able to get data off of it with the data port. But the PC cable didn't come with it, and I can't seem to find it online (at least not for less than US$65+).

I could easily make the cable myself for dirt cheap since Flytec is nice enough to provide the pinouts of the cable in the manual, but I have never seen the socket that Flytec uses.

So the question is... does anyone know what type of socket that is and/or where to source one? Or is it a Flytec proprietary jack?