Thai silk is not really sought after that much, so breeders in the U.S. just doesn't breed them as much. They also have a lot of issue as in term of health which really makes them a pain in the _________.
I believe there are actually a few local breeders in the states that have done it countless numbers of time. Just got to come across the right person. If your looking to buy Thai Silk, they are all over in the U.S. being frys most of the time. Check on Flowerhorncraze see if they can pin point you to that person that breeds them. I know that Julie from Flowerhornsfrombeyond is selling Thai Silk frys at the moment still. You can buy it from there if you don't mind the shipping.