This ground has been covered previously in the MMD.  See

    http://mmd.foxtail.com/archives/Digests/199701/1997.01.28.02.html

for the complete text of what I wrote at the time.

CITES provides a mechanism for international transportation of materials
such as ivory, tortoise shell, etc., and with the proper forms, such
materials can be moved legally between signatory nations. (The U.S. and
Canada are both participants.)