The E85 Mix App is a good bet. The E85 station search app isn't doing me much good in my area. Even doing a google search on my computer didn't turn anything up. With the stations that were listed, not only did they not have flex fuel but didn't even know what it is! How can you work at a gas station and not know what E85 is and whether or not you have it? My search today turned out to be a joke.
I finally found one with flex fuel but when I got there, (30 min later) their pumps listed their flex fuel as 50-83%. I tried asking one of the attendants to narrow it down for me so I could make an informed entry into the calculator. He says, "I don't know, whatever percentage they bring in that day." (really?)
Definitely thinking twice about upgrading to an E50 tune. Even if I had an ethanol sensor, how can I know how much flex to put in if I don't know the percentage? SMH