[Hallicrafters] Adding A SO-239 Bulkhead to a SX-122 Antenna

[Chuck]

I want to install a SO-239 bulkhead in parallel with the antenna screw 
terminals on a SX-122.
There is provision made on the rear of the chassis to do so.
I once had a SX-122A with the SO-239 installed.
I removed the pop-out cover and installed the bulkhead fitting and 
connected it to the A1 antenna solder point.
However it is not that simple. It does not work with the ground link 
attached to or removed from the A2 connection.
I noticed the manual calls for an AN Type SO-239 connector. I Googled 
this and found nothing.
Can anyone tell me how to do this?
Tnx es 73,
Chuck KA6UUP