There is the BRCA clubs page,
http://www.brca.org/Clubs/club%20frame%20page.htm
lot of clubs have pages, but not all clubs are listed - its a good start.
Also a good list of clubs at racechat, both these are a mix and not just 10th off road.
http://www.rcracechat.com/vb/forumdisplay.php?f=10
and some area sites at
http://www.onetenthoffroad.co.uk/clubs.htm
Should keep you busy
