Have you considered the chance of bezoars or ambergris?

Stalking a dragon for the chance of the animal expelling such things would be a terrifying endeavour.

My insight on your question: if nothing else, some crazy fool would tout a dragon's kidney stone as an invaluable ingredient for alchemy or some obscure potion or the cure/treatment for some disease, just like rhino horn or pangolin scales or deer penis for chinese traditional medicine. So considering this possibility alone, even in our current reality a dragon kidney stone could be sought after.