I'd never heard of Bandcamp before yesterday, and I'm not sure what it is - is it for unsigned bands to release their material to an hopefully adoring public? Don't know. But I do know that downloads of mp3s are free from their page, and the pages include material by Marc Bolan and T. Rex. I've really no idea if the downloads are legal or not, so caveat liberator.
They have a download of Marc Bolan's unfinished and unreleased (while he was alive) rock opera, Billy Super Duper, as well as several sets of demos, including Tanx demos and Electric Warrior demos. Enjoy them while they last!