I don’t know of any ongoing, organized small groups of bators of any kind. What I am aware of is small, informal gatherings happening privately. Those may or may not include poppers, but I assume a few do.

The best ways I’m aware of to organize or find small groups is through craigslist and bateworld. search for “stroke” and “buddies” at craigslist and search for “Seattle” in bateworld.