There are restrictions on the freedom of brewers (and other suppliers) to advertise the availability of their products at a particular retailer. For one, they generally cannot initiate the transfer of information–someone must request (such as by clicking “Find Our Beer” on a web page) the information first.
A California ABC industry advisory details one way that a brewer could advertise the availability of its product at a particular retailer proactively. §25502.2 authorizes (until 1/1/16, at least) a supplier to “employ or engage” a person to sign autographs for consumers at an off-sale retail licensee’s premises (a liquor store or bottle shop, for example), and to advertise in connection with the event, including the beer to be featured, and to list the name and address of the retailer in the advertisement. Restrictions include no pictures of the retailer’s premises, and the listing must be “relatively inconspicuous in relation to the advertisement as a whole.”
This privilege may be used twice per year per retailer and must be registered in advance with ABC. While limited, this could be an effective way for small breweries to engage with their local fans (the brewer(s) themselves could sign the autographs) and to announce the availability of their product at a new location (or just to raise awareness about pre-existing availability). If the brewer were to make a special release beer for the event (or make an already popular seasonal beer available first at the event), that may make it even more successful.
Small brewers ought to be able to just send out a Tweet whenever they’re newly stocked at a store or put on tap at a bar, especially those that only self-distribute and are available in limited locations. The market works better when consumers have full information with which to make their choices and there would be no risk of the harms the regulations seek to prevent. For now, though, they are constrained to making use of the limited exceptions such as the “autographing event” one mentioned here. Since it would cost little and foster relationships with local retailers, small brewers should try to make use of it while it is available!