I don't know the whole issue, but I know there are some severe restrictions on import and use of ivory, the result of the massive "save the elephants" campaign. This would, at the very least, make real ivory grips pricy and scarce if not possibly illegal.
Actually, ivory is not a good grip material as it yellows, shrinks, and cracks over time. Saving elephants aside, the better plastics are much better, last longer and retain their color.
Jim