Any modelling program that has curves should allow you to create a (half) profile and the revolve (or lathe) it to create a surface.

Failing that you could get much the same effect by starting with a cylinder and then scaling individual rings to achieve the desired shape.

Once you have an object export as OBJ and import into Bryce.

Finally if your that way inclined, you may be able to use booleans to put something together.