If you can't find someone in our community(we have a couple of artists, I believe), I'd recommend
Fivver. You can commission drawings from people online there. 5 dollars will usually get you something bare bones like a black and white pencil sketch with more money getting you things like color, backgrounds, and additional characters. My experience with it so far has been pretty good. The artist is encouraged to respond pretty quickly and I don't believe the funds are released until you sign off on the finished project. All the same, most of the illustrators I've commissioned from seem to be pretty accommodating. I didn't use it as a NWN portrait, but Fiverr is where I got my
drawing of Beldor done.