Pete, I got my system from a shop around the Chatuchak area years ago. The shop is still there, but it is quite common to find these things in the major garden centers now. The two popular brands available in Thailand are Rainbird and Gardena. I got the Gardena stuff.
One was a programmable timer that ran for about a year on one 9V battery, great for when you're away for a few days. Also a filter unit and an assortment of drip heads (different flow rates). Haven't tried the Rainbird but it seems quite popular. They are fairly expensive but worth it in my opinion. Will try to find the name of the place I bought it from, but I think you should be able to find it in your neck of the woods.