The Band of Starpower is an accessory that increases maximum mana by 20. It can only be found by smashing Shadow Orbs in the Underground Corruption or from Corrupt Crates, making it nearly unobtainable in Crimson worlds. However, the player can create an artificial Corruption biome (from materials acquired from a Corruption world), create a fishing pond inside the artificial Corruption biome, and fish for Corrupt Crates within their Crimson world. Overall, it is much easier just to create a new Corruption world (assuming the player has previously defeated the Wall of Flesh- which allows them to choose the world evil freely).
On the Mobile version, they can be found in Living Trees, making them possible to obtain in a Crimson world.