Is there an on-line resource to locate stores? I now there are several in California, but it's a HUGE state and narrowing down closer stores within my area is a bit of a struggle. Any advice?

Someone started a map way back when the game launched for players to pin their local stores supporting the game, unfortunately they were using some sort of free service with an access limit and uh...yeah that capped out pretty quick, so now you can't access it anymore. I'm not aware of any new initiatives to collect that info, though I've been out of the loop the last month or so. Far as I know, the recommended method would be either checking on the L5R Discord or Facebook groups, there may even be an existing FB group for your local area that can help point you in the right direction.

Normally I'd also recommend checking the Organized Play section of the L5R page here on FFG's site, since they had store event dates listed for some of the bigger OP programs...however that section seems to have...disappeared? You could also try the list at the below link, it's over a year old but might be another starting point at least.
https://www.fantasyflightgames.com/en/op/l5r-lcg/elemental-championships-venues/

EDIT: Nevermind, the OP section is still on the product page...I'm just a goof and clicked on the first L5R product listed, which used to be the LCG. Apparently FFG reorganized and now the RPG is the first item listed. 😅

domo arigato gozaimasu.