As far as I know, all village stores in small villages (strontian, cannich, shiel bridge) sell meths, but some do not
For instance, the store in Dalmally doesnt. However, the pharmacist in Dalmally sells meths in smaller bottles, so my advice: think again and look out for hardware shops, filling stations, pharmacies, or after opening hours, even try farms or residents with a well stocked shed.
By the way, the bottles the stuff is sold in are quite tough, so no need to bring a fuel bottle...