All About Fish in Pleasant Hill sells, I think, 3 different kinds of live rock, and prices are pretty decent for an LFS. Aquarium Concepts (the new store is pretty cool) also has live rock for sale, as does Aquatic Gallery. I think theirs is $6/lb or so. Connie's Tropical Fish in Castro Valley sells Fiji LR for $4.99/lb if you buy 10 lbs or more - although it's been a while since I've been there.
Mermaid doesn't have a retail location open currently, as far as I know. Last time I went to Dolphin a couple weeks ago, you couldn't walk into their fish section, but if you knew what you wanted, they could get it for you.