I can only suggest a good Thai brand of peanut butter to buy, not where to find it outside of Chiang Mai.
Rimping markets in Chiang Mai carry two Thai brands of sugar free PB. I prefer the one called Tida's. I don't recall the name of the other brand but will try to remember to look for it next time I'm at Rimping. Both are sold in 1kg plastic bags so you would need a good size jar/container to hold the PB. I rate Tida's as being on par with Adam's PB from USA.