ARMIN
I think I've found what you need. Of course, the problem with that piece is that YOU HAVE TO KNOW WHAT TO CALL IT IN ORDER TO FIND ONE. I've been searching for years to be able to attach one to my PAIA Theremax! FINALLY -- I think this is it...
If I'm correctly understanding what you need, this looks exactly like the phalange/fitting on the BOTTOM of a standard Etherwave. their description addresses another use, but take a look.
http://www.podcastingnews.com/items/On-Stage/MUPTMO2.htm
It's described as follows:
OnStage TMO2 Threaded Table Mount
Do you mic your amp? Buy this handy, all-metal accessory, and a gooseneck, too. Mount it on your amp, and get that extra mic stand out of your way forever! 5/8 in. flange with base holes on 1-1/4 in. mounting centers.
Manufacturer: On-Stage
List Price: $8.00
Online Price: $4.95
I hope this helps. Please let me know.
-Kip