If I was you I would try to get in touch with some kinde of ministry (try maybe textile, sport manufactures, industry) of these countries (Thailand, China, Vietnam) and tell them what you're up to and that you try to source materials in their country.
I think if you go trough these official ways you're more likely to strike gold! And since the info would have been given to you by officials you probably would get what you want without the usual questions: is it a real factory, web site...
You can PM me later for my details!
