Although I have little experience with South California specifically, I do have some experience in finding experienced, reputable breeders. There are a lot of "common" and simple answers here. Facebook and Instagram are actually your friends. Many dog breeders are small business owners. They do not have a marketing department and limit themselves to what they know, many of them end up having only a Facebook page or group that they stick to. Facebook groups of the local area and pet-related groups for the local area can help you find good breeders.
Secondly, Googling several key phrases like "[insert dog breed] dog breeders near me", "local dog breeders", "[insert dog breed] near me", etc. can help you find pages for breeders near you. This isn't always fruitful but may enlighten you to other online avenues that your local area may use to communicate about dog sales. Some social media platforms are more popular per geographical location than others.
Lastly, and not always guaranteed to have a result, is ask local stores. Pet stores, especially small stores, sometimes know local breeders. Local breeders are likely to need pet supplies, make contacts, etc. Pet store employees and owners see many more dogs than most of us and are more in-tune with the local pet community. Even if they don't know a breeder for your specific dog breed, they can sometimes offer to keep an eye out. If that breed were to come in later, they may ask the owner if they know a good breeder in your area. As mentioned, this doesn't always give a result, but I have found local breeders, rescuers, groomers, etc. this way.