Blibbet is making a list of FOSS groups in Seattle, and a few that sound like possible groups we could collaborate with are OpenStreetMap [1], Code for Seattle [2], LocalWiki [3], and Techno-Activism 3rd Mondays [4].
[1] http://www.meetup.com/OpenStreetMap-Seattle/ [2] http://www.meetup.com/Code-for-Seattle/ [3] http://localwiki.net/seattle/
PCS is a professional tech writer group, not a volunteer/community group, but it might be a source of local writer contributors. http://www.stc-psc.org/wp/about-us/ http://www.stc-psc.org/wp/the-stc-puget-sound-chapter-meeting-minimalism-in-...
There's also many writer-related Meetups: http://creative-writing.meetup.com/cities/us/wa/seattle/