OP is not a glowie, this gets talked about frequently on Calguns... the CA resident buyer needs the rifle to be converted to a CA-compliant configuration (non-roster and fixed mag or featureless) before it can ship to CA. That often involves changing muzzle device, stock, grip, mag release/lock, etc.
Several manufacturers will do this on new rifles... JP has shipped me several rifles in a CA-compliant configuration and were great to work with.
It gets harder buying a used rifle that would be CA legal with the correct parts but is currently out of state in a non-CA compliant configuration.
Always easiest if the buyer can buy the necessary CA-compliant parts and send them to the seller to install, then the seller can can ship the rifle in a CA-compliant form from their FFL directly to the buyer's FFL in CA... but many sellers don't want to take the time to do the parts swapping.
I'm not sure what shops will act as an intermediary for the conversion work, you'll probably have better luck asking over on Calguns.
EBR Works in AZ used to do CA-compliant intermediary conversion work; they did a couple transfers/conversions for a local friend about 6-7 years ago, and they used to be a member here on SH, but I don't know if they're still around and active.
