In attempting to learn more about the use of a "clammer" or even its historic training application I've been doing lots of google searches, and have had a really hard time finding much of anything (or anything at all really). Makes me think that there must be another term out there for this particular little bit thing that I just have never heard of.
The back story on it for Pia is that it came from the BO and in turn was something she picked up while training with her super-fancy-national-champion-olympic rider. SFNCOR suggested it as a method to keep smart/energetic horses distracted and playing, and also a method to lighten a horse in the hand without adding leverage or any severity to the bit currently in use.
I also know that BO was only able to obtain one up in Canada, which makes it slightly less than accessible, but I would think that unless the cannucks have gone completely crazy and disconnected themselves and the great white north from the interweb, that I'd theoretically be able to find one of these things online.
Anyway, I have no documented history, instructions, advertisements, suggestions, opinions or merchants for one of these, but I do have the BO and SFNCOR saying that they have "tried it" and it's "worked."
Frankly I don't much care what it is or where it came from if it makes the mare happy and it doesn't cause any pain.