This statistics tutor worked hard to show a way to make a 3D bell curve. The addition I would make to his idea is that I would have velcro so the blocks would stick together when stacked. Legos (the large size) might work as well.
It goes to show, when students get to college they need to have access to mathematical tools. We need to make sure our students realize APH materials are available for purchase by them and by the college.