Was wondering if I can find it in the States:

the clamp is a slit ring of may be 4" OD, made out of
1/8 or so, spring-tempered steel. Works wonders when clampling
elaborate/intiricate woodwork.

Is used extensively in Russia - this is where I saw it.
Doing extensive searches in US catalogs didn't show anything
even remotely similar ...

Trying to avoid having to make my own (1/8 drill bent with a home made
bender, heat-treated).

The ring has to be as close to ideal circle and be planar to work
the best.