I'm not confident that there is a cape item out there, but perhaps you could increase the chances of getting one by finding a cape object/mesh somewhere online and asking someone to convert it into an item if that makes sense? And if it requires purchase, to ensure that you're willing to purchase that object/mesh yourself? I think there might be a tutorial or guide on how to do that yourself somewhere if you even wanted to try! Converting objects/meshes to items, that is.