In the Golden Age, the Amazons used 'Amazonium'. Of course, nowadays it would be unfairly compared to Vibranium. However, Themyscira could still be rich in natural resources and that out of a sense of duty and curiosity they began to build their own technology to better protect themselves, explore possibilities and gain a greater understanding of the world. Hippolyta has a magic mirror that can view the outside world, the Amazons could go on expeditions to the outside world where they take inspiration from existing technology and reverse engineer better technology.