Unfortunately, without a rental it's going to be hard to travel to the stores listed because they're not close to public transit.
If I weren't busy on Sunday, I'd offer to pick you up in the East Bay (taking BART from SF is very easy) and then travel down south going from Aquatic Collection -> CA Reef -> Neptune. Diablo Corals is simply too far out of the way to suggest heading there, especially since they don't offer anything unique compared to the other stores on the list. If another reefer who lives in SJ can pick you up at the Fremont station, you could do the reverse drive, then be dropped off at the Hayward BART station for your return to SF.
The only reason I bring it up is because a couple of years ago, a reefer who lives on the east coast was attending a conference in SF and was interested in seeing my tanks. We knew each other only from our conversations on RC, and it was really nice to meet him in person. He jumped on BART, I picked him up in Oakland, and we hung out at my house for an hour or so, then I dropped him back off at BART.