You can buy them at any Bike shop. http://www.unicycle.uk.com/shop/shopdisplayproduct.asp?catalogid=125
@provenrad started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
You can buy them at any Bike shop.
http://www.unicycle.uk.com/shop/shopdisplayproduct.asp?catalogid=125