We have had 3D globes being made on here in the past. This one I recall was very successful.
http://www.cartographersguild.com/sh...your-enjoyment

We also had some posts about the pneumatic 3D terrain tables by Grumman or similar which look well cool.

I can machine 3D terrain in 2D but I have only tried it once. It worked well but it takes ages and ages to do it with a fine cutter. Not sure what its like to make one with a 3D printer tho.

Personally I think it would be possible and easier to harden up one of those exercise balls with resin and then use some kind of plaster, fiberglass, car body filler or epoxy putty on top to make a globe.
E.g. http://www.exerciseball.net/bell-fit...cessories.html