I was thinking E-85, relatively available. But I get your goal state, I use the same logic for lots of other stuff. Nothing like being able to walk in to a grocery store and buy what you need...
In the late 60's Buick was playing with lean burn, they had a fancy ignition and carb to try and control detonation.
The Klotz or Motul additives are not badly priced especially if you purchase them in the bulk sizes. Mix alcohol 50/50 in the water tank it will reduce the needed volume of water..
Just thinking its a cool idea, if you can slay the detonation dragon...
Dave