"...but there's an absolute ban on importing ivory to the US."

This is not true even for African Elephant ivory, at least not yet. [1] There is also legal ivory trade in Mammoth and other animals such as wart hog that can easily be found at gem shows, knife and gun shows, etc.

I talked to a guy from the Ukraine at a knife show who was selling Mammoth tusks recovered from Russia and apparently had quite a time at the airport but he was able to bring in his supplies for sale.

[1] http://www.fws.gov/international/travel-and-trade/ivory-ban-...