Since the chances of you being able to find copies of all your covers on-line, and purchasing new cases for all of them might be expensive, I think the best solution would be to hunt down whoever took your cases and kill them, KILL THEM, then bring them back home.
If you simply lost them without any thieving, simply ask Satan to bring them back to you. He's usually in a bad mood when I talk to him but there's no better way to achieve these sorts of things.
The most realistic thing might be to wait for
www.dvdcoverart.com to come back. It's down right now but I hear it will return, and they have shitloads of covers.