Most of the base fuel sold for that would be CBOB of RBOB, which is designed to be mixed with 10% fuel ethanol to reach the designated AKI octane rating. There's also different California reformulated blends. It really doesn't make much sense to do otherwise. I guess it's possible though, but I'm not sure what incentive there would be to have some sort of custom fuel blend for something like 6.5% fuel ethanol.
www.eia.gov
Now there is one issue where fuel ethanol is supposed to be between 2-5% gasoline as a denaturant, just in case someone thinks it's a good idea to use it as a cheap way to make their own vodka. I've heard that some blend in something like 10.25% fuel ethanol to make E10 on the premise that it will result in a maximum of 10% ethanol since there's that little bit of gasoline.