no shortage of places to buy it in OC. the LA board will help with specifics, but in general any asian store (like Ranch 99) will also carry banana leaves - usually frozen. They work very well. And, of course, just about any market in places like santa ana, gigante or not (staters) will probably carry both banana leaves and achiote paste. Look for the banana leaf either in the fresh or frozen section. could be in either.
Get thee to Gigante (Anaheim)or Any Mexican Supermarket!! The Achiote Paste(El Yucateco Brand Perferably - it comes in a block) will be in with the Meat Section and condiments section (Where the Mole is). The Banana Leaf in the produce section and if they are out, you can make due with Frozen (They have that as well).
You can also pick up your pork there for SUPER cheap too!
Enjoy!! Remember to dip the tortillas in the juice when making the taco! That's the BEST part! :)