The Black Panther film finally reveals the origin of Vibranium. If you don’t know, the Captain America Shield designed by Howard Stark is made of vibranium.
Vibranium is found in abundance in Wakanda and this material was used by the previous Kings of Wakanda to build a country that was very advanced in technology.
Wakanda is on the African continent. This is where the Winter Soldier is treated so that he can be released from the influence of Hydra.