Does Maya have an option like this? If the option could alllow selection for the number of levels and the size of the bands of color that would be really helpful. I saw Maya's vector renderer but it doesn't offer the amount of control zbrush offers unfortunately, there is no control over the size of the bands, and it limits by number of colors instead of levels.
You should just render it normally and then apply a posterization filter over it in AfterEffects or Nuke. If you don't want to do that, you can either code/script your own shader or modify the toon shader that comes standard in Maya to your liking. Preferrably, modify the toon shader and then try adding a texture or similar option to it.