Tasdad sells them.. but last i heard he was still trying to figure a way around the charger fitting... maybe cut them a slight bit shorter
Most of the time they will fit, but there are some batteries/chargers that you may have issues with.
Here's a pic of a skinned e-cig.

The biggest issue I have is that the Skinz fade pretty fast. Within a week, only the darkest areas were visible.

It's actually more faded than this makes it look. It's basically white with a few blue lines now.
I am looking for a new method/material/ink/whatever that will make them last longer. For now, these are more like temporary tattoos for e-cigs.
Anyways Back to topic...Have you been able to airbrush any e-cigs yet? I'd love to see them!