There is appoximately 10,000 shooters is North America. There are new clubs started up Internationally in Sweden and Germany and Australia. Recently the Cowboy Mounted Shooters of American (CMSA) has just signed an affilite deal the the AQHA. Any Registered AQHA horse competing can get points from the AQHA.
Cowboy Mounted Shooters site in the USA: http://www.cmsaevents.com/