For a source of ivory or any other key covering or other related
materials, contact Michael Morvan at  http://www.pianoandorgankeys.com/

Michael is a real expert in all areas of key restoration, especially
ivory replacement.  He is great to work with and will sell any material
to you.  His web site is a treasure trove of information on how to do
expert key repairs.

Jurgen Goering - Piano Forte Supply
http://www.pianofortesupply.com/