If you want a store that’s customized for the Orthodox Jewish community, look up places in Fairfax, Pico-Robinson, and just LA in general. Ask a random Orthodox Jew in the street if you will!
If you’re just interested in black pants/white shirt/suit…try Macy’s…Kohls…JC Penny…many good deals and nice clothes. I think the majority of my white/black clothes are from Macy’s. They have 2 shirts (short shirts too! for the summer months coming up…LA gets pretty hot!) for 50$. Good shirts, too!