Age of piano keys

I’m new to this and I want to know how I can document the age of
piano keys I scrimshaw on so that I can sell the jewelry made from
them. They are off old pianos and I’m as opposed to the killing of
elephants as anyone but can’t see throwing the ivory away when lovely
things can be made. Does anyone know the rules of selling this type
of thing and how I can make it legal and above board?

Thanks
Shayna