The bones...most of the time I order them online. Because I live in an apartment complex, and I don't just happen upon deceased animals often. Otherwise it seems kind of stupid to pay for bones. Well, except for the whole gross factor. I have tried that a time or two as well...
I take it all back, it's way easier to just buy them. Not very expensive anyways.
Check out The Bone Room, and Moscow Hide and Fur. [The Bone Room even has human bones ]