Well I do have an idea where to put them (actually two places though one is on the eastern half of the map which I've never finished) but as for CR, I'd say CR 15 with Treasure: None would balance the item.
The logic being a CR 15 creature ought to give 22,000 GP of treasure, this way the item is now a use-activated item of something between Resurrection and Raise Dead (Resurrection would place it at just under 15,000 GP) or can be used to replace the material component of True Resurrection as an alternative option should you find a priest with such capabilities.
Of course, I'll probably make them even stronger to put them more on the scale of legendary creatures aiming towards CR 18ish, or with "Young" "Adult" and "Elder" categories and give them either other harvest-able organs (I like power components) or something. Make them war with the white and silver dragons that share their mountain peak homes.