Marin has some great business networking opportunities.
Most cities have Chambers of Commerce, with regular mixers and business networking events.
Full Chamber Calendar for the North Bay Counties:
http://thechamberlink.com/north-bay-counties-calendar.html
Mill Valley Chamber
http://www.millvalley.org/future-events.html
Novato Chamber
http://business.novatochamber.com/events/
San Anselmo Chamber
http://sananselmochamber.org/calendar.html?Type=2
San Rafael Chamber
http://srchamber.com/pages/MixerSchedule
BNI SF Bay
http://bnisfbay.com/events.php
Referral Institute SF Bay
http://referralinstitutesfbay.com/index.php/en-us/calendar/