There are a few vendors that have these in stock including Amazon...
Here is the Samsung OEM Part Number...
Looks like the book cover will soon be available as well.
Samsung Part Number: YA-C1C7NBECXAR
Most of the online vendors either show "on order" or "special order" for the book cover.
I recently bought a Rearth slim case and am quite happy about it. I wouldn't mind getting one of these book covers once they become readily available.