These lands are indeed from the game Blood & Magic. However, that game was adopted in canon and is now the most detailed source of lore on this region. There was a page-long writeup in the Grand History of the Realms as well. The area also appears in the Double Diamond Saga, which has since been determined MOSTLY non-canon.
One of the FR wiki admins, BadCatMan, is probably the best source of information on this area. He also did writeups for the region over on Candlekeep.com a couple of years ago.
The Sempadan Forest is not far from the southern Capital city of Anok-Imaskar, Tempat Larang, which is detailed in an Oriental Adventures module, OA6: Ronin Challenge. Anok-Imaskar was a successor state of Imaskar and basically created the foundations of Shou Lung & T'u Lung in Kara-Tur as well as originally claiming the lands that you're asking about.
The area is populated by a pseudo-asian people (kind of east indian) called the Mar. They were visited by Ffolk and Northmen from the Moonshae Isles who ended up dominating their culture.