I goto The Home Wine, Beer, and Cheesemaking Shop
locally. They are just across the valley from me and it's a big store/supply place. They have almost everything you'd want.
There is a very small party supply store on the top end of the valley but I forget the name. They just have kits and supplys but low on the homebrew grains etc.. It's more of a party supply store but one of the owners is a homebrew board member for the Maltose Falcons.
There is also Culver City Brew supply on Sepulveda blvd in culver city. It's not that big but does have what you'd need. I'd go there but the other two places are closer.
I'm making a run to Ontario tomorrow to pickup some bike tires I have on will call and running over to morebeer.com retail store afterward.. if your intersted in going, pm me and I'll pick you up on the way through.