These plugs can be bought from Allied Electronics for about $12.
To find the plug/socket you need, go to the manufacturer's site, Bulgin click "Buccaneer Connectors", "Standard Buccaneer up to 10A, 250V", and choose from the array of available configurations.
I need a second Low Profile Flange Mounting PX0767/S plug so I can use my ST2000 in 2 different boats.

Most of the pictures of plugs shown are 3-pole, but they are available in 6 pole as well.
The male end for the AutoPilot cable is also available,

as are the little screw-on caps that seal the socket when not in use.

This is the source of this info.
I've ordered the plugs and will follow up with either a "yay" or a "doh" depending on the results.