One place to find batiks in Thailand is along Sampeng Lane at the sarong shops. Two famous shops are Emchit and Vibul Kit. The shop numbers go in order. Even numbers on one side, odd numbers on the other side of the lane. Vibul Kit is #96 and Emchit is nearby. A sarong is 2 meters (a little more than 2 yards) and costs approximately 100 baht. It is great for quilting and if you are looking for Thai fabrics, get some of the other sarongs too. Some have small prints, and some have plain colors with border prints. See below for batiks from Emchit. Vibul Kit carries the same line. As for other places to buy batiks, I will let you know when I find them!
Batiks in Thailand