From what I've been told, it was invented sometime in the 1970's, but I had never heard of it until I came here. There could have been any number of reasons as to why that is. There was a war going on, and dark creatures of all kinds were joining Voldemort's side. The Ministry could have kept the discovery under wraps because of this. Or the Daily Prophet decided not to report on it as there was just too much going on. Or they could have been only contacting families of registered werewolves whom they believed could have afforded it. Or it might have just been me not paying enough attention in Potions; it never was my best subject.