What on Gaia's Green Earth? Purchase bound spirits? Spirits aren't property! Someone has the audacity to say that they are.
First thing is first: no vampire spirits, werewolf spirits, or mermaid spirits exist. The idea of it does, but they will never exist. The people who are trying to sell jewelry for that purpose is seriously trying to rip you off and make money from it. They're frauds; scams.
However, if you do want to work with spirits, they have to want to work with you willingly. I cannot stress that enough. You can create bonds with spirits. There are other ways to work with them besides binding them to a piece of jewelry and demanding things that they don't want to do.
On the other hand, there are other things like thoughtforms that you can create, and have them help with you with magick as well.