Maybe you could get some other mustelid native to california instead? They wouldn't have 2500 years of domestication behind them, but e.g. stoats (short-tailed weasels) are sometimes kept as pets, and are native to california (and much of the northern hemisphere). Likewise the (much closer to ferret-sized) mink, various american mink subspecies are native to california.
The marten is an other california-native mustelid, though I don't know if they can be tamed easily.
One last option (that I know of) could be the tayra, it's apparently easy to tame and although it's not native to california its range goes up to mid-mexico. Could be more acceptable than invasive europe-originated ferrets.
Speaking as a former ferret owner, I would advise very strongly against trying to domesticate a wild mustelid. Given the right circumstances, even pet ferrets can be dangerous, and they have a nasty bite; running foul of a wild one would probably be a bit like falling into a wood chipper, except that a wood chipper won't run up your pant leg.
The marten is an other california-native mustelid, though I don't know if they can be tamed easily.
One last option (that I know of) could be the tayra, it's apparently easy to tame and although it's not native to california its range goes up to mid-mexico. Could be more acceptable than invasive europe-originated ferrets.