Check Cosco, however most cooking extracts will have alcohol in it, another thing you could try, which I am sure they will have in the produce section, is buying a small peppermint plant and using a mortar and Pedestal, the plusses are that mint plants tend to grow like weeds and the flavor can be as subtle, or strong as you its much easier to control, in leaf form.
Costco doesn't have it. I regularly purchase my Kirkland Signature Vanilla Extract (35% ethanol by volume) from them, not to mention my soymilk itself.
My issue with the peppermint plant grinding is the peppermint isn't strong enough. The extract I got from that Nugget Market tastes terrible (tastes like alcohol) with a peppermint overtone, it's really bad stuff.
The Andes mint milk shake I get from Jack-in-the-Box are on an exponentially higher degree of strength, which I can't seem to replicate with extracts, peppermint patties or , likely, the plant itself.