Where can I buy vault voyages in Sea of Thieves?

I'm curious, where exactly can one purchase vault voyages in the popular game Sea of Thieves? Are there specific merchants or locations within the game world that offer these voyages? And what kind of resources or in-game currency do I need to acquire them? As a seasoned pirate, I'm always looking to expand my treasure hunting horizons and these vault voyages sound like a thrilling adventure.