I think we should start a thread called Thailand. Bangkok is of course the centre, and the large shopping malls such as Siam Paragon and Central Chitlom have the main designer brands.
For more adventurous fragrances, Comme des Garcons can be found in the Erawan Plaza. (Chitlom sky train station).
There is not much available in terms of niche fragrances, as far as I know.