Look em up on xbox.com and see who has them. if they are active send them a msg. doubt you would get those gt though. And if you do be prepared to pay $200+.
If you weren't such a skid, you'd look up the tag on xbox.com, then come to the realization that KanyeWest is banned for life. Also, Yeezy is online right now, so invite him to a party/private chat and ask if he'd sell the tag, but from the activity of his account, I don't think he would.