I found a cover for the K4 at Amazon, and it is in stock:

Marware-Eco-Vue-Kindle-Touch-Cover

It is a bit pricey at $34.99 but that is less than Amazon's cover, and the Amazon cover won't be available until November 15. The one caveat is this cover will also fit the K4 Touch so it will be a tad big on the K4 NT.

Oh, and for those of you asking about the K4 SO option: This morning I had a $5 off on $10 Amazon purchase offer waiting for me on my K4. I took the offer and saved $5 when I purchased this cover.

I estimate I've saved enough $$$ through special offers I've received via the K3 since I bought it 3 months ago to easily pay for the K4 I just bought. It is definitely worth putting up with a few subtle ads to get the savings on items I would have purchased anyway.