An interesting item, though its very niche. It seems that it would best be provided by some NPC to assist in a very specific mission. Otherwise I would add a few more trollish bonuses to the item to have the PCs keep a hold on it. Go to Comment
The S'krae Lifeforms (Intelligent Species)
Okay, armour created from Ivory is not too far-fetched - lacquered wood and boiled leather both make reasonable armours. I could see alchemists involved in the preparation of the substance but not in the actual construction of the armour.
Apart from Moons comment on Ivory being bone (its not, similar, but different) his comments are spot on.