TexasCHLforum.com

Texas DPS teaches a course on this subject to their troopers. Some of this material was used in my CHL course. If you know someone it might be possible to obtain some of their training materials.

Yerasimos' post has some good suggestions: Marc "Animal" MacYoung's book looks like a good start. While the normal "HR fluff" may not be exactly what you want, some of the same approachs and techniques could be valuable for de-escalating a potentially violent encounter.

I think a practical course that does some role playing excerises would be way to go. This link might be helpful: http://www.twu.edu/o-ll/mediationfaq.htm