Hello.
I'm in this band called Infirmity
www.facebook.com/infirmity

We are trying to get more shows but are having a hard time
finding promotion companies & booking agencies.
Does anyone know of a good place to find (like a list) of booking agencies?
Or does someone at least know some good promotion companies & booking agencies
in southern California? Thanks.

You have to go to underground shows, become familiar with promoters, then ask.

Or that's how Durvasag got it done.

Yeah, local networking is the most important thing you can do. As far as promotion and booking agencies, you're probably not going to find anyone willing to work with you unless you've already made some sort of name for yourself.

Ask local bands who the promoters are, like their pages on Facebook, and show them your music. If a promoter doesn't have anything to listen to they won't bother, so make sure you have something, even a decent-quality live recording like what my band has.