Are there any off-road clubs in your area. Do some searches online for clubs around major cities near you. If you find any, and they have some sort of online presence (even social media), reach out to them for suggestions.
Try Diablo Off Road in Walnut Creek, they don't appear to be a serious off road shop compared to Arabia's Automotive, Inc in San Jose. But they have done suspension work on my 05 Rubicon and I have been please.
Not particularly close to OP, but the thread title says "Northern California" which is a very large place. (Perhaps the title should be edited to read "East Bay" or "Bay Area".)