I got a "repro" back card for barnacle in the army swap. It was just an image of each side of the backcard printed out and put on cardstock. I got it from TwilightWhispers. I don't know where she got the image from though.
You'd probably need to make sure you have access to a printer than can print larger than letter size paper, because the one I received is slightly smaller than an actual backcard just due to the size it could br printed at.