You could try searching for Forgotten Realms at sites like Archive of Our Own and Fanfiction.net but I'm not sure how much luck you'd have finding what you're specifically looking for. I've heard that ff.net has been on a steady decline as far as quality is concerned and all of these places tend to be filled with specific character-oriented content rather than stories celebrating the realms as a whole.
Are you looking for leaded or unleaded,aka erotic vs. none erotic FR stories?
You can find for erotic FR stories you can try Greyarchieves, Naked Blades, and I think they're used to be a erotic story site that posee as a Temple of Sharess.
For none erotic you might check the white archieves.