The eBay ivory ban in Australia relates to the CITES Convention
(Convention on International Trade in Endangered Species) which was
adopted by Australia in 1976.  Most countries forbid trade in ivory
produced after 1975, the date of the original Convention.

The United States law is stricter than most; it forbids trade on
ivory less than 100 years old (i.e.; pianos with ivory keys made after
1908).  Note that this 100-year rule covers "international" trade only.
Ivory sales within the USA on more modern pianos are legal so long as
they were made before 1975, and I assume the same is true in Australia.

You can check the Australian law at the Austrian Dept. of Environment:
http://www.environment.gov.au/biodiversity/trade-use/cites/index.html#cites 
For other countries, see http://www.cites.org/ 

Exporting any ivory requires CITES paperwork from the country of
origin, and proof of the pianos age.  (I make a copy of the pertinent
serial number page in Pierce Piano Atlas.)  A fee is charged according
to your country's law (usually around US$20-$30).  You can download
your country's CITES paperwork from the internet.

The eBay rule seems in error, as it is not completely illegal to sell
ivory in Australia.  Check with your CITES Authority and for ward their
response to eBay Australia.

Regards,
Philip Jamison
Pennsylvania