While true ivory keys still surface from old pianos etc, given the general stupidity of some well-meaning governmental functions, it is best to use bone when making replacement parts. Some auction houses will refuse to put up for auction anything with ivory, no matter the age. Other auction houses have been known to pry out the "offending ivory escutcheons" doing great damage to otherwise pristine clocks. I have had several of these to repair. So, bone is my choice of replacement material. And the last group of keytops I bought from eBay was all celluloid, not ivory, so there is that too.
I use a piece of masking tape placed over the escutcheon recess, rub around the edges with a pencil, then transfer the tape to my material and cut to the rubbed line. Makes a good starting point and additional shaping will be minimized. I also CNC route some of them, but usually getting the layout and drawing done accurately is more trouble than using the masking tape approach.
These examples were all from a couple of NY auction houses 3 or 4 years ago. The auction ads showed the clocks with the escutcheon in place, so they did all this damage themselves. I have made maybe 50 of these in the recent past. So, bone yes, ivory no if you are planning to resell the clock. I have also been making parts from the faux ivory products used for gun grips and the like. Just finished making several wheels for a couple of ivory clocks, made the replacement of both bone and faux ivory. I have also used deer or elk antler material. Also, clean dog chew bones, made of steer bone, can be had at your local pet stores
View attachment 674163
View attachment 674164
View attachment 674165
View attachment 674166
View attachment 674167
View attachment 674168
View attachment 674169
View attachment 674170