Ed Fowler sells a nicely made one in the US, Repro magic in britain sells a really nicely made brass one ( www.repromagic.co.uk/
) and it is called PentaLock (It is the one I currently use when working in comedy clubs).
It has some advantages over Key-rect but Key-rect also has some advantages over a gravity lock like this one. The cheif one being that you can fail with it if you are not careful and the only way to avoid failure is to hold the lock in the correct position yourself while the participant trys the key. With Key-rect, you do not have to hold the lock while the participant opens the lock.
Paul Alberstat http://www.mindguy.com