Have a look on the British Show Horse Association website - if you go into the rule book area. then there are contact details for judges most of whom will be people who do lessons and pretty sure the contacts for both the above will be in there.
Steph Wheway is based in Cheshire and has a website. From the little experience I have of the showing world Cheshire seems to be a popular area for show producers - there seems to be loads round there!