Target seems to have the Batman Assault on Arkham steelbook in stock as of the time of this post:
Shows as $17.99 and says Steelbook in the item description, plus shows the correct item picture. I ordered one with some other items and will see what shows up by the end of the week.
Just received my package from Target and it was the steelbook for Assault on Arkham. Packed in a box, even.