Here you go, found it at last! £12.50 inc postage:
http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=230426137648 He also sells a "kit" for £29.50 which is the adapter with a pressure-switch banjo bolt, if you want to run it with brake lights for the road:
http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=230426137632 HTH.