However, I'll try to find it. It wasn't a cell-shaded mod, but a clever use of the Q3 shader tool on a particuler custom player model. In fact, the first instance I can find of cell-shading on a Q3 model was in July of 2000. A couple of Dreamcast games had already tried that, and the author of the Q3 model in question specifically references them as an inspiration.
As for the Q3 model in question, it was "Honey" by Connor O'Kane. It's <a href = "http://www.planetquake.com/polycount/info/quake3/honey/honey.shtml">here</a> on polycount's archives.