Dear Nikita,
They are used a lot in www.insex.com from what i've heard. (smile) Also can be obtained from online bondage stores.

I've been looking for the classic picture on the Net, of a Malay/Thai. girl suspended by cords and an anal hook, while taking a Protein feed. As it's not copyrighted, but, Murphy's Law, can't find.

The nearest my Ex. got to doing that to me was trying to lift me by twin dildos. "OwwWW!" Was my pleasure.