There are some good ‘how-to’s’ on youtube on how to make your own slipcases, as well as info on how to make them / a custom box set in the An Index & Help Thread for Case Covers, Disc Labels, and Fan Art.

It is also worth checking out some of the generic cover sites listed in the Index thread for alternative art for the 2011 SE blu ray releases (and there may be some quality cover art in the Index which you could use or edit as an alternative too).

Good luck with it - let us know what you come up 👍