Up in Chiang Mai the government runs the milk coops which collect, process and then distribute raw and pasturized milk. I'm pretty sure that is the case wherever there are going to be enough cows, so not sure about Bangkok or south. Another option in Chiang Mai (for raw and pasturized milk) is Thai Danish, across from the zoo. The Govt milk coop is just south of the city on the first ring road, after it crosses the third ring road (Chiang-Mai Lampang road). There, 10kg of raw milk is 230 THB (min. 10kg). Prices are comparable at Thai-Danish though one can buy a smaller amount (5kg).