Maplebar...doh...man...trying to remember the name of the place I used when I lived in San Diego. Some place down in El Cajon that did a lot of custom work. Did really good work for me. The deal with the cat is that they can replace it if you are past a certain mileage OR your cat is clogged...or they think it is defective or getting so. So they can almost always come up with a reason to replace a cat...and then simply justify it by saying the cat was going bad. As long as a cat goes back on to replace the OEM unit, high flow or not, it is essentially legal.
That said the testing I have seen is that high flow cats offer minimal, if any, gain over modern cats. Older brick style cats flowed like crap but the modern honeycomb ones in use since the mid-90s flow very well. I put a CarSound (Magnaflow) cat on my Tracker simply because it was cheap and quality, I doubt I saw much gain from it over an OEM replacement cat.
Those bills will only become laws if you guys do not get out and vote against it. There are enough car enthusiasts in California, of any political party, that would be adversely affected by a potential law as stupid as this that I doubt it could pass if enough outrage was shown. Hot Rodders, boy-racers-rice rockets, offroaders, rock crawlers, mall cruisers, restoration guys, shops, businesses, fab shops, etc etc etc etc.
Michigan had a bill to do something similar and also ban "derelict vehicles" (IE-your parts vehicle or project that you do not keep in a garage) in visible site about 4 years ago. This is Michigan...you would not beleive the groundswell of anger and outrage that came up from the masses. It never even got to the floor of the house other than as a sidenote that the sponsor was withdrawing it.