I've been looking for one of these a long time, but was unable to find a printable model anywhere. I finally gave in and heavily modified the terminator skull found at: grabcad.com/library/terminator-head
and made it a single, solid mesh, learning how to use blender in the process.

Be aware, printing one of these on a self replicating printer may be a really bad idea. Hopefully the end of the world isn't open sourced ;)

The original was printed on a Fablicator. Fablicator.com