I don't know of any specific nurseries there, but my experience in Southern California has been that any old Home Depot or even Walmart will often have great prices on some things we non-californians would consider exotic. Bird of Paradise should be very easy to find at the former store. If not, you should be able to find a plethora of non-chain nurseries to check out.

Happy Hunting!

Unfortnuately, a lot of the mom and pop type of nurseries in LA have been swallowed up or have gone out of business due to competition from big box stores and (until recently, anyway) escalating real estate prices. Armstrong garden centers seem to carry a varied selection, but now that I'm not living in LA anymore, I'm not sure what Angelinos would consider a great selection of landscaping and container plants.