I don't know of any groups either, Flycraft. But since there are so many climbers, you may just want to organize a group! Portland would be a great place to do that, since the tree climbing adventure possibilities are endless.
My suggestion is that you contact all the TCI members privately, tell them what you're trying to do, and give them your phone number. I'll bet you can get something started. On our website (in the Treeclimbing menu) you'll find other help for organizing a club based on the Atlanta experience.
Good luck, and thanks for posting.
Patty Jenkins