So, after months of searching and more e-mails and phone calls than I'd like to recall, I was ready to give up on finding pond liner.
Today, Ms. AC and I went up to the big nursery center at Khok Kruat, about 10 K west of Korat on the road to Bangkok. They have a couple of big lined ponds there and we hoped to find someone who knew where the liner was purchased.
Turns out, they sell it right there....
Boy do I feel dumb.
There are two kinds for sale:
PVC and HDPE (High Density Polyethylene). The PVC comes in rolls that are 1.8 meters wide. This is not wide enough for me so I'd have to glue it. The HDPE comes in 3.6 meter width; plenty for me.
Based on what research I've been able to do, both are strong, resist tearing and have good UV resistance.
I'm leaning toward using the HDPE to avoid having to glue a seam.