Didn;t know there were any. I just asked the infant school head teacher if I could go on the waiting list to be a lunch time supervisor, and got the job! This was 20 years ago, so things may have changed.
I am a (relief) lunchtime supervisor (must be the new name for it!) local school put up job advert in shop and I got it! You do need to fill out a CRB form Criminal Records (school will tell you where to get one if they don't already have some to fill out) and if you are ok they will send you a disclosure form with all your details on it ( usually within 4 to 6 weeks) you can't work with children without it.