My personal ethic is to never use animals killed for the purpose of my art. I get my skulls from the following sources-
* Rat skulls are from frozen rats used as reptile food - I use the head for the skull then give the body back to the shop to be fed to their snakes.
* The rabbits and pigeons have been routinely killed as pests - I have a contact whom I pay a nominal amount for them, otherwise they are incinerated.
* Ebay, where I always ask questions before bidding to ensure I don't buy from trappers.
* Road traffic accidents.

I realize this is of course not everyones standard of ethics. if you are vegetarian/vegan (i myself am not) the use of any animal product is more then likely not for you. This is simply my own personal opinion when concerning working ethically.

I also take commissions at no extra charge and am more then happy to work with a person to get exactly what they want. This gives you the chance to have a one off design made specifically to you.