In the movie 'Black Panther', where did 'Wakandan people' find the rare metal called 'Vibranium'?

Vibranium is a rare metallic ore with energy-manipulating properties. Theorized to have been first deposited on Earth by a meteorite 1,000,000 years ago, the material has long been hypothesized - by many scientists who have had ample chance to study it - to be extraterrestrial in origin. Captain Marvel inadvertently proved this theory to be true during a scuffle between survivors of the Builders attack and the Spartax Empire who had relocated them to Torfa where the latter had begun poisoning the planet and the refugee population by using an unsafe technique to secretly mine Vibranium for use in rebuilding their fleets. However, although Vibranium was once mined on a number of planets, all of those mines have apparently been exhausted. As a result, aside from the planets Earth and Torfa, there are no known stores of Vibranium left in the Milky Way Galaxy.