I used a Trangia with alcohol, 9 months in Africa. If used for how you describe, you shouldn't have a problem - a liter should last a few weeks. You start looking before you are totally out and you'll find more - it may take a few stops to find.
You won't find clean-burning methelated spirits though; sometimes all you'll find is purple 'rubbing' alcohol. Try pharmacies or groceries - the location(s) change as you change countries. Here in the US, I go to the paint department of hardware/home building stores.
Chiang Mai, Thailand