I'd forget about using real ivory, for a multitude of reasons.
There are some astonishingly good-looking (and feeling!) keytop
materials available today, that have no relation to the horrible,
shiny, too-thick-and-cheesy-looking types put on many pianos,
just a few years back -- currently used materials that countless
pianists would prefer to play on rather than real ivory.

Look in the back of a Piano Technicians' Guild journal for ads
from the many key-recovering services.  Ask them to send a sample
of whatever they use, a price list, and some references.

Gordon Stelter