Any well stocked garden center should have it. I think one upscale place (as I remember) was called Armstrong's--they would be a likely place to check. I saw one in Anaheim, not far to your south. There were a couple others too, Bluebird or Bluebell ? not sure of the names--something like that.
I don't know what Brands they sell but look for (or ask for) Calcium Sulphate (Sulfate) powder or granule. Also, look for Powdered or Flake Sulphur. Those would be your first choices. Another soil acidifier you'll likely see is, Aluminum Sulphate (Sulfate) and they'll probably try to sell you that one,, especially if they don't stock the first choices. But I don't recommend it because Aluminum is freed up in the chemical process and it's residual in the soil and IS NOT an essential plant nutrient/trace element. Further, with bulb and tuber type plants, (in layman's terms) Aluminum ions can plug membranes of the roots preventing the uptake of essential nutrients and trace elements.
Aluminum Sulphate and excess free Aluminum ions have little or no affect on other acid loving flowering shrubs, however. While you're at some of these places, ask if they can run a pH check for you. It shouldn't be too costly, I wouldn't think.
Edit note added: Rick, I guess I started typing just before you finished up. Which leads me to a question I have--Do you suppose one can eventually get 'too much' Calcium in the soil ( people with hard water wells, etc). Nice, informative link, by the way!
