I am a Marriage and Family Therapist seeking internship opportunities
in Alameda and Contra Costa Counties (Northern California).Please
provide any lists,directories, websites, publications, or other data
pertaining to agencies that offer adult, couples, or group, mental
health services in this area.

Try www.capic.net.  It's the California Psychology Internship Council.
 But I think your grad school program is probably the best bet for
resources.  It might also help if you include if it is for a master's
or doctoral leveld degree, if you already have the degree or not, or
if it is for licensure.