For Thailand, S. P. Somtow (
Wikipedia) is the premier sfnal author, and he's very good and a winner of multiple awards, though much of his work seems to be out of print.
There are some
reprints via Smashwords (couponable @ Kobo), fortunately for some of the books I would personally recommend.
- Jasmine Nights is a non-sfnal (outside of magical realism elements) coming of age novel featuring a friendship between a Thai boy from the privileged classes and an expat American, loosely based on Somtow's own experience growing up as an Eton and Cambridge educated distant relative of the royal family. I really liked this and it's one of my favourites of his, which I happen to own as a hardcover.
- Dragon's Fin Soup is a collection of several of his sf/fantasy stories mostly set in Asia and showcases his style fairly well. I also have this in paper and it's a good selection, though perhaps not among his best. So you might be better off trying his Opus 50 which I haven't read, but is a retrospective anniversary collection with selected essays, poetry, and short stories which are supposed to have been selected from among his best.
There are also some really good Thai modern culture/ancient folklore-based short stories of his which appear in early volumes of those Gardner Dozois and Ellen Datlow/Terri Windling-edited Year's Best Science Fiction/Fantasy & Horror anthologies, some of which you may or may not already have as e-books if you've been getting the reprints.
Also, the reprint company which handles his Smashwords stuff offers a freebie sampler which contains a few full short stories, including one from Somtow himself:
The Bangkok Writers: Tales from the other City of Angels