There are several compositions that produce the man-made Ivory - a couple even have actual Ivory dust as a part of their makeup.
Linen Micarta is also used, but not as much.
I do know, though, that laser engraving will "burn" its pattern - leaving the lines a dark brown - similar to actual aging, yet not as dramatic as inking them would be.
A pleasing effect.
I'd ask a couple of the manufacturers - Eagle, Ajax, Tru-Ivory - and see what they say.
Good Luck,
Scouts Out!