The live music scene here stays pretty active year round, and a reliable way to browse upcoming rock concerts in San Diego is through a dedicated site built for exactly that, check the listings here https://myrockshows.com/location/223-san-diego-ca/ . It focuses specifically on rock and metal shows, pulling together dates from different venues across the city so you are not stuck jumping between individual box office pages just to see what is coming up. Smaller club gigs tend to sell out fast once word spreads, so keeping an eye on a site that is built around those genres helps catch announcements before they disappear into the noise of bigger event aggregators.