Jeez, now your askin.
I don't think i've even seen a friction clamp in 15 years or more, was with SGB in UIE clydebank at the time.
On a lighter note almost every scaff i've met since then thinks friction clamps are like big weights, long stands or the good ole Sky Hooks.
the only place i saw advertising them is
Scaffolding Supplies.
Also found a Cape & SGB site on about them but Southern Africa is a bit far to go for a clamp don't ya think. it did give some figures for the chains and a few sketches but not really much technical info its more an erectors guide.
SGB/Cape site