Here are some searchable databases for positions with labor unions and community groups:

Union Job Board lists available jobs and events in the labor movement, as well as information and updates.

http://www.unionjobboard.com

Union Jobs Clearinghouse lists available staffing positions, apprenticeship opportunities, and educational opportunities around the U.S. and the world.

http://www.unionjobs.com

Idealist lists job and volunteer opportunities in many different not-for-profit fields.

http://www.idealist.org

Good luck!