What are the chances this could be a never before seen episode?
If you mean a filmed, live-action episode... zero. They underdelivered for S2 because of the strike/budget problems (they were meant to deliver 26 episodes, like every other season, and only managed 22. Including "Shades of Gray"). If they'd filmed another episode, it would have gone out.
At a stretch, I suppose some sort of storyboard/reading of an unmade script might
be possible. That's the limit though.