Well, for Kindle DX you can get this here:
http://www.amazon.de/igadgitz-Hartsc...7306871&sr=8-3
Hardcover: YES
Booklike: Not exactly, but maybe sufficient, don't know if it fits on the 90X
Unfortunately I can't recommend the Premium covers mentioned by marty63 because the plastic fastenings are a bit weak. The cover itself is great, but after my 602 fell from my bedside table ( ~ 25 cm) the top fastening broke and I had to replace it by something indestructible (Glassfibre compound, not easy to do)