They're out there, but the process is corrupt, opaque and ridiculous. Unless you own some sort of classic or you have money to throw away it just isn't worth the risk and investment. This is coming from me, a guy believes in the concept of emissions regulations and is a closet tree hugger...
You basically have to pay a private company (there are two of these ARB accredited companies in the whole state) who gets to do whatever the f*** they want, charge you what they want, and do business however they want, in order to award you some little sticker that goes on your door jamb saying that you are federally emissions compliant. The process costs $6500-8500 for a little bit of fuel pump tuning and the addition of an oxidizer, bringing it to some invisible standard that the owner of the company won't share with you. He writes you the quote on a sticky note in scribbled cursive. He will not provide you paper work and will not tell you what parts or process he will use to bring it to spec. All you're paying for is the sticker. After that since you actually do not have comply to any smog standard, you can completely uncork it, turn up the fuel and roll coal all over Southern California if you wanted to.
Without that sticker it's a roll of the dice and completely up to whatever DMV assclown you get, it depends on whether they know the laws, whether they care about the laws and how the manager who has to sign off on your short VIN number interprets the conflict between BAR and ARB requirements. If they aren't satisfied you get sent to CHP, where it is once again up to the whatever CHP officer you have the privilege of being saddled with who is then in charge of your case. When I was sent down this rabbit hole the CHP officer actually knew less about the laws than the DMV guy I got, threw the book at me and called me an "idiot" and an "a******" in front of my then 4 year old daughter for wanting to register the truck in CA, and told me that I needed all of these notes from BAR and I had to install air bags and antilock brakes, ect and needed to get ARB to sign off. After I spend several months debunking his BS I ended up getting stuck on ARB and decided it was better to sell the truck and start over again.