I'd love to help by heartily recommending Gail Burt and her stellar crew at my own local store,
Metropolis Comics in Bellflower ... but that's across the L.A. basin from Van Nuys and the San Fernando Valley. So others will have to suggest. Golden Apple Comics has a great rep.
As to other advice: Get a "Thomas Guide" map-book for Los Angeles and Ventura Counties (in light of where you're living), immediately upon arrival, and keep it in your car at all times. You cannot navigate this twisted nightmare of local streets, arteries, freeways, and hundreds of municipalities without one.