I'm not sure about Ca laws about ammo but there are many sites that sell ammo.
Cheaperthandirt has pretty good prices sometimes.
Natchez is another. Midway sells ammo too. That's three of many.I use Natchez most the time but that's mainly because they send me emails about sales and if I see a good deal I get some. Most the older established sites are not too bad. cheaperhtandirt went a little higher than I though they should have when the ammo crunch was in more of a full swing than it seems now.
Look around. You can compare prices and you might find a deal getting it by the case rather than a couple boxes. Plus the shipping is pretty high on ammo so if you're going to buy that way you will want to get enough to make the shipping worth your while,.