I am not 100% on this, but the trend I have seen throughout the U.S. seems to dictate that octane ratings for a given geographical area depend on the state and the elevation. Generally speaking, higher elevation areas such as Albuquerque will have lower octane ratings. As far as California goes, I believe there is nothing higher here than 91 octane.
Every state I have been to in the eastern half of the country has 93, however as I traveled west, I noticed the octane ratings decrease a bit. Whether or not this is due to state laws, elevation, etc.. I couldn't say for certain. This is just a trend I have observed throughout my time in differing states.
From my travellings over Christmas, I noticed that East coast has 93 and some places actually had 92 octane, wtf? Illinois is the farthest west place I noticed that had 93 still. Missouri has 91 octane, and I'd imagine it's the same for most of the midwest states west of the Mississippi R. As far as a website, I only know of a website that gives current gas prices for your area, I don't see any octane mentions, but you may be able to find some.