Who makes the Tone arm with swing out damping trough that the head shell sits in?????

Townshend? http://www.townshendaudio.com/the-rock-7/

The damping trough is actually part of the Townshend Rock turntable, not the arm. Townshend makes an arm with the "outrigger" headshell built on, but the outrigger comes with the table, and you can use any arm you want with it (other than an ET, of course!). The Townshend U.S. distributor often uses a Helius Omega arm on the table.

It's brilliant!  It would actually be even easier to make a trough for the et. It's on my todo list. Maybe in 2030 I'll get to it. 

At the headshell is the best place for damping, and Townshend is the only way to get it. A damping trough for the ET would be awesome!