I haven't gotten around to fussing with mint flavor in ice cream yet, but from my extraction experience I can suggest a couple of avenues for the home scientist to pursue in quest of something other than straight high-test mint oil.
A simple method would be to layer fresh mint leaves with your powdered sugar in a sealed environment and heat gently to express the volatile terpenes to permeate the sugar. This will be a subtle essence and might not correspond to what is normally considered mint flavor. Herbal, florals and menthol flavors might predominate.
For those who really like to play hard, make up an ice bath with dry ice and alcohol and chill some Everclear 190, to which you would add your mint leaves. Stir for a minute or two, then strain and evaporate the leachate until an appropriate strength. This method will pull more oil and leave a stronger mint flavor, which you can vary with the length of wash. This will be a clear solution, if green is your goal do room temp, but you'll lose complexity.
Of course, wear gloves and eye protection.
