I have not bought Parmesan at Corti brothers so I don't
know how much better it is than other Parmesan Reggiano's.
I would think any good cheese shop or upscale grocery
in L.A. would have reasonably good Reggiano.

I usually buy the stuff called "2 year export" or similar
but I don't really know what this means. Specialty
cheeserers will have Reggiano from specific farms. It's
usually better, but not by a huge margin.

Steve