I bought my xB used and it didn't have the xB logo, but Ocotillo on this site was kind enough to send me his! I just cleaned the back of it, got some 3M tape, and stuck it on there. Maybe someone else on here has one laying around they aren't gonna use.
I am getting ready to remove my xB, if you want that. I'm still thinking about whether I want to completely debadge and remove the Scion on the rear. If you want the xB, I'll send it to you as soon as I remove it.