SFBAAPS (San Francisco Bay Area Aquatic Plant Society) is an aquarium plant club, some fish trading, too. Our next meeting is at Aqua Forest in San Francisco. Meeting locations rotate through the Bay Area. http://forum.sfbaaps.org/index.php
SFAS (San Francisco Aquarium Society) is more fish oriented. Someone messed up their web site. They have meetings once a month. Several members of SFBAAPS are also members of SFAS, so you can usually find out the next meeting date at the SFBAAPS site.
Sacramento also has a fish/aquarium/plant club. I am not sure of their schedule or location(s).