ICOM Headset Adaptor Plug

I've picked up an ICOM IC-A5 handheld that I'm going to install into the
avionics panel of my Fly Baby as a semi-fixed installation. I picked up a
headset adaptor for it, but I don't like having those big clunky headset plugs
as intermediate connectors. I want to implement Jim Weir's "Karmic connector"
concept, but if I do that, the radio install will involve five connector sets.

What I'd prefer is to wire up my own adaptor to the radio. However, I'm having
a devil of a time finding the right plug that fits into the headset adaptor plug
on the radio. To the eye, it appears to be a 3.5 MM plug similar to the
standard 1/8" walkman headset plugs, except its four conductor. I found such a
plug at the local electronics store, but it only fits in the radio a bit less
than halfway. Visually, it looks dead-on, but apparently is slightly larger
diameter once one gets past the tip. Nokia cell phones have four-conductor
plugs, but they're a bit smaller.

I'm loath to cut up my current headset adaptor, since I'd like to keep it as a
backup and the blessed things cost $60 each.

So: Any idea where I can find a plug? ICOM doesn't list the plug alone on
their web page, nor do they provide the connector ID.

Ron Wanttaja