Hi Jo,
That's the link that i have found.
I also found this on the web :
Companion Shows and Match Nights
Smaller shows such as companion and match nights do not need to get permission from the Kennel Club before inviting a judge. These shows are an excellent start for novice judges to hone their skills before moving on to Open shows.
If you are running a KC open show then the judges need to pass a course i think

It's only very basic though.Then you need to put your CV out there and wait to be invited to judge.
Companion shows are very different although you should only ask someone to judge if they are competent lol !