I used to visit Sacramento on business probably now, over 10 years ago, until
they closed the facility (to my chagrin, as Sacratmento is a great place to visit, with Old Town, the RR museum, and highway 49 gold country and Yosemite just down the road), and I had then tracked down two O scale shops near the now closed Air Force base. I have since used Sacramentp as a base to visit California, much preferring flying in and out of there than LA or SF.
I think both O scale shops were gone when I visited after the base closure. North on 99 out of Sacramento still advertised is The Western Depot at Yuba City. At that time there was a shop in Roseville I think I visited once, too. I did visit a tinplate shop in downtown SF once, too. These seem to turn over faster than car salesmen, so I would raid the shop indices in the back of OGR and as many current hobby magazines as you can get hands on, identify locations, and make a list.