I'm interested in the sport as well. There is a training location maybe 10 minutes away from me, but I'm waiting until Chase has a reliable "stay" before we start. Other than that I don't know much. I hope there are some people on here that do.
Dock dogs is so much fun! I've had the pleasure of watching some competitions and talking to dock dog owners. Around here, there is no official "training" place. Basically you just find a dock and train them on your own. When there is a nearby competition, you can usually pay to practice on their equipment during a certain time. Then when you think your dog is ready, you can just start entering(hoping for the best I guess!). I hope that it gains popularity because it seems very confusing to get involved in.
Some places probably have more proper training places for dock dogs. I would try going to a close competition and ask competitors how they got started.