I haven't seen any NA beers in the local 7/11 - Family Marts. I haven't looked in the supermarket yet. I suspect you'll be able to find something in 4/5 star international-type hotels' bars. Supposedly Clausthaler and Paulaner Thomas Brau NA have been spotted in Bangkok.

Light beers have only just started making in-roads here so probably a few more years before Boon Rawd comes up with a NA beer.