I found the webpage for The Union of UK Unicyclists which led me to the discovery of a couple of local (or local-ish) Unicycle clubs.

Further I found http://www.unicycletips.com/ with compendia of video and other training material; if you still think unicycles are mostly ridden by clowns in circuses, you need to check out what Kris Holm does with them:

• “body armour test” (.wmv)
• jump test (.wmv)
• trailer: one tired guy (.mpg)
• trailer: defect (.mov)