Low Flow Shower Fixture (California Compliant)

[Mikeiii]

My understanding is that showers in California now need to be 1.8gpm. I used a Hansgrohe 04230000 S pressure balanced faucet in the last shower I remodeled years ago. I was going to use the thermostatic version of the same valve in my next bathroom. When ordering online they will not ship a system with that valve to California because it is not compliant.

Question:
-Does the valve have anything to do with the minimum flow rate? Can I just order the valve separate and buy a compliant head?
-Any recommendation on a good low flow shower head?
-Is there a better or more reliable valve?

Thanks

Mike