I'm also in California. I haven't bought any for years, and don't know any specific brands, but I would look for glass jars or those short little deli containers. Try the Whole Foods produce section near the refrigerated dressings (another possibility would be near the hummus and similar items). Some of the larger/fancier Vons (aka Safeway in Central/Northern California) have artisan cheese display cases, and they have usually have specialty spreads there if you can't find any in their produce area near the dressings or fermented/pickled refrigerated items. If you are in Southern California, Bristol Farms stores have an amazing selection of specialty foods. Maybe Trader Joes has it. I haven't seen it there, but I've never looked. The cheese or produce sections are most likely, near the prepared dressings or refrigerated sauerkraut.
I have seen raw horseradish root in the produce section of well-stocked produce departments, and you can make your own prepared horseradish. If you go that route, it will definitely clear your sinuses. :) I grew it once, and digging the root was intense - every time a section of the fragile root broke off I would get a face full of fumes, and I was using a full sized shovel, so my face was a few feet away!