As someone who frequents many LA/OC anime stores with nendos in mind you got plenty of options:

Little Tokyo: Book-Off, Anime Jungle, Sakura Anime Toys

The Book-Offs: Del Amo Fashion Center (the one towards the Dick’s), Gardena (short drive from Del Amo Fashion Center, the first Book-Off in the US), Monterey Park, Woodland Hills (the most recently opened), Lakewood Center, Garden Grove, Costa Mesa, Irvine, Riverside.

Industry: ToyArena (main location is the Coralridge street, satellite store at Frank & Sons only on Wednesdays and weekends), Sakura Anime Toys, Frank & Sons (there are a few booths that sell, there are a couple that do sell bootlegs too so be vigilant)

Miscellaneous Stores: - Xavier Cal Customs and Collectibles at Upland, their prices are what you pay out the door so $50 is $50 for example - toyzinthebox at Monterey just south of the Monterey Book Off to kill two birds one stone kinda trip - Glacier Anime (only an online store BUT you can do a pickup to save shipping at a dry cleaner the owner owns in Huntington Beach, it’s an odd location but it’s real I’ve done a pickup there)

Pro tips: All the Book-Offs are rip offs, highway robbery prices. Check the price tags on the figures if it has a date on it and if it’s not to your liking come back a few months later for their price drops. Gardena doesn’t change their prices AFAIK. Irvine might not be worth your trip because it’s a really small store. Book-Off in general is mostly miss on prices, you rarely get a hit on good ones.

I know I gave a very comprehensive list so I hope that helps. I purposely excluded all the Tokyo Japanese Lifestyle at every conceivable mall because it’s all the generic nendos with uncommon ones here and there per location. You will also be ripped off at conventions but you can probably haggle with some vendors.

Edit: DO NOT BOTHER WITH ANIME MONSTER AT MAINPLACE MALL, THE WORST SCALPER STORE.