i can think of three things you can try (if you haven't already).
try www.imdb.co.uk and look him up there and see if there is an agent listed.
see if there is an official site - there is bound to be a link.
you will certainly find him listed in 'spotlight' which is a multi-volumed collection of artistes with their agent's details.
rather than paying �100's for a copy, try calling spotlight and asking them. they are very helpful. i don't know their number off-hand but they are based at 7 leicester place, london, WC1 (just off leicester sq, next to the prince charles cinema).
good luck!