I got these in Taiwan in 1989. The manufacturer asked for my input on them and I made a few recommendations (most notably, the double pinch bolts and the stepped profile). I never saw the parts on the market in the US, and I am fairly sure these are the only two survivors.
It should be noted that Scott Towne had a similar idea in the early 80's that he called "The Enforcer," though Scott's did not have an integrated seat clamp. Aside from the stepped profile and double pinch, the product was in development before I hit Taipei, lest anyone think I was trying to rip off rather than riff off of his earlier creation.