The only 93 octane seen with some repeatability around here is BP, and not all have it. And to be blunt, between the price and the fact that monitoring what my ecoboost truck perceives as the octane has shown that 93 octane in the flavor found here is not worth the money. Two brands of 91 octane routinely deliver the same performance (Shell and Speedway).
And before anyone comments on it, yes, we do have several distinct sources of fuel available in this market, so there can be differentiation between brands most of the time.