The original map came from Map Resources. The product I bought at the time (over ten years ago almost now) was cheaper than their current sets. Licence terms were great (could re-distribute as long as it was not in editible vector form).
You can currently buy individual maps from them, so something like this is what I started with:
mercator world Of course, if I had to do it all over again, I would build the map using
GMT, so that I could render maps in any projection/perspective/scale. I keep threatening to do this some day, but probably never will.