I've been looking at the Gundog Club online, they have courses (group and one-to-one) as well as taster sessions. I haven't done it yet as I'm saving up for a course, plus my dogs recall needs more work first, so I don't know how good they are...

Training Your Gundog

I also think you might be able to find gundog classes through APDT trainers, if you try their website for trainers local to you, it should list what activities they teach, whether agility or gundog.