I can't link to them from work, so no URLs, but, try these.
Bioware's official site (I think it is nwn.bioware.com)
Neverwinter Vault (not sure of URL)
I know for a fact there is a version of U1/U2/U3 out there (Saltmarsh / Dunwater / Final Enemy), 'cause I have it installed on my computer.
There are also at least some of the D&D 3.0 adventure path modules.
Although I will say that I think the core NWN story (starting with the Wailing Death but getting much more complex) is overly looked down upon. Yeah, there is a lot of "go here to get X in order to help Y", but that is true of all these types of games. If you are willing to slog through Chapter 1, things get a lot more interesting by the end of Chapter 2, and especially in Chapter 3.
Plus, by Chapter 3, your character is a total bad-ass.
Shadows of Undrentide (the first expansion) has a more refined, tightly written story. It also has some pretty damn cool uses of the game engine to support the story -- so I would definitely check it out. You should be able to get it for $10 or so these days.