Haven't ever found one honestly. Cheetah showed me one to ask Qs about someone's contact trainer. It was UK based but I was going to join till I was creeped out you have to use real first and last names as your forum name.
I've been on mighty mites for sports in general for dogs under 16" it's okay, but I haven't found it super useful.. Other than that most aren't sports based, let alone agility based.
I'm on the bark list, it's the yahoo group for the AAC but it's unofficial, more for Qs about new stuff and brags than help to train..