I picked up Knights in the Nightmare from newegg.com about a year ago, and It came with a digital download for Yggdra Union off of psn.
I don't think it mentioned it on the box, so you might take a gamble and buy a new/sealed Knights in the Nightmare from somewhere, and perhaps you will get the psn code too. Its a good idea, if you don't mind Yggdra being digital.