Look up statistics on market share of beer brands. I just glanced at Google, and saw that for at least some relevant years there are number available for both amount of beer produced, and amount of beer sold through supermarket chains. That doesn't narrow it down to the West Coast USA or get you from "Anheuser-Busch" to Bud, Bud Light, Michelob, etc., but it's a good global picture.

Additionally, I'd start playing the footnote game. Find some recent scholarship on grocery stores and comb the bibliography. Whatever looks like it might either have your information or get you a step closer, get the source and comb its bibliography. (Unfortunately the books I've read on the topic pertain to Australia, England, and pre-1970 America, so I don't think they'd be a great place to start.)

Finally, looking at the bibliography of Building a Housewife's Paradise: Gender, Politics, and American Grocery Stores in the Twentieth-Century, it appears that Tracey Deutsch was able to get ahold of major chains' annual reports for various years going back to the 1920s. Maybe that's a route to explore if your footnotes take you to a dead end and you're not satisfied with the overall numbers?