Hi Mike,
I'm just up the road from you in M'Dore. I looked through my parts and sadly I couldn't find one of those plugs, that short one seems quite unique to the EC-10 and I haven't seen it elsewhere.
I really like the EC-10 and have a few of them, on one it had an L/O buffer added to drive an external frequency counter with the IF offset applied.
All of my EC-10 units have had the RF transistors replaced due to the tin whisker problem. I used AF178's which I bolted in using the method shown here:
https://www.vintage-radio.net/forum/...d.php?t=139849