You probably already researched him, but here is what I found from his campaign website as his supporters.
Midwest Values Political Action Committee(Al Franken)
http://midwestvaluespac.org
Take Action Minnesota
http://www.takeactionminnesota.org/
They are associated with the Joyce Foundation
http://www.joycefdn.org/
Coalition for Democratic Values: No web info found
Minnesota League of Conservation Voters
http://www.mnlcv.org/
Along with other assorted union, teacher and government worker organizations