I have a set of piano ivories that I "harvested" from a piano my mother was having renovated, many years ago. They have remained unused for over 40 years, due to the thinness of the pieces. Aside from decorative inlays on m/l rifles I haven't found a use for them yet. But, maybe someday ................
Fossilized walrus and mammoth is legal in the US.
Again, it's not truly fossilized. It's only in the first stages of fossilization. A more accurate term for it is "mineralized". A true fossil is like rock. Mammoth ivory can be worked just like currently harvested ivory. But, it usually has streaking and colors from the beginnings of the mineralization processes.