[Solumina]

It is not illegal to sell human remains, there are a few states that ban the import or export of them but there are no federal regulations about it.

That being said I think a necklace that just has a bone hanging from it (human or otherwise) or two bones made into a cross are just plain boring, I can't think of any reason why someone would buy such a think other than "ooo it's made of people, look at me I'm so dark and spooky", which is just dumb.