I recently did a Day of the Dead wedding cake and I used the Wilton Skull pan to create a cake skull tier. It’s pretty large though, maybe larger than what you need.
http://www.amazon.com/Wilton-Dimensions-Nonstick-Skull-Pan/dp/B003XKZSDI
Jenniffer White, Cup a Dee Cakes - http://cupadeecakes.blogspot.com