Most States hold conspirators have to a) be in on it and b) take an overt act to further the conspiracy. It would be a huge huge stretch to hold any buyer accountable as a co-conspirator imo. Maybe you can prosecute them on mail fraud (which is a nice catch all the way the statute is written) or something else along those lines because its likely that if they were in Israel there were countless Federal issues involved.
Maybe other people have other suggestions as to what to prosecute them on. But i cant see the end buyers being nailed on conspiracy. And while ignorance of the law isnt a defense - like its been said before, you would need to prove they knew they were buying stolen goods. The middle men on the other hand are a different story.