Having seen fisheye lenses up close (including a decent substitute for the Nikkor used on 2001), I can tell you that duplicating a fisheye will be a lot of work. There is something about a real lens that is hard to duplicate - especially in acrylic.
The most common approach is to trim a hemisphere down so you have something the approx. diameter and height. Problem is, the acrylic hemisphere has a consistent (and thin) thickness. A Nikkor lens is darn near solid.... You could try stacking a different lens (or lenses) inside that trimmed hemisphere.
Also, Hal's look - that hot yellow core followed by some rings of orange/red - that will be hard to duplicate as well, because part of what you are seeing is light bouncing around off of the interior elements in there.
I was asked by a friend of mine (who, ironically has worked with and is friends with Douglas Trumbull) to build one for him, "just to have next to his computer". I researched the cost of the real lens (and tossed that idea out the window unless I win a lottery). I've tinkered with some substitutes, but I think getting some sort of real lense that approximates the shape is the way to go.
Karl's re-discovered research may provide the impetuous to look at this again, though.
Gene