i got one from here...
i actually got this skull form this company and it's pretty nice and worth the purchase.
the only thing i would say about it is i don't like it with the vertabrae cuz i can't move it around to as many angles as i would like...
on the other hand you get an good idea about how the vertabrae connect to the skull.
this was also the cheapest place i found, and it was also recommended by my current anatomy/figure instructor.