The ivory laws in place now make it illegal to sell ivory across state lines.
Robert, is that only raw ivory that's illegal to sell or ivory in objects, vintage as well as modern? I know eBay won't even allow a seller to list an ivory object for fear it is made from post-ban material.
another reason to ban mammoth ivory is that they are very close to producing elephant/mammoth dna hybrids jurassic park style, and with some careful breeding every succeeding generation can be closer and closer to pure wooly mammoth. And if they do so, it will probably be a protected species for a very long time, or maybe forever.