The Silver Marches tome, nearly every 2e tome that covers the North to some degree, and I think there was a little tidbit about the Moonwood in Lost Empires of Faerun. There's not a great deal of significant information, and most of it is spread throughout other entries on areas in the North.
I can't be more specific at the moment because I'm away from my books.
I did some digging the other night and Sage is absolutely right - Silver Marches has the most recent information (and intriduces the focus on the Malarites that infest the place). The 2E sources are pretty vague and talk about elves being present. There isn't much detail at all, I'm afraid - but great opportunities for you to do "your own thing".
-- George Krashos
"Because only we, contrary to the barbarians, never count the enemy in battle." -- Aeschylus