There is usually a CPPS pre-season ref clinic each year.
To be frank, though, reffing is a case of learning as you go in most cases. Most events are short of refs so do not be afraid to ask.
You'll meet a lot of people and make some good friends along the way. But you do need a thick skin, because you can't please everyone.
The PSP has probably the most advanced and well-publicised ref training program, with clinics before each of their events. Lane Wright runs a tight ship, and with Paul Richards on his staff things are getting even better.