Just in case the Nolty didn't work for you, there's also the clear Midori B6 cover over on JetPens. I have used the A6 version of this and it's great, comparable to the Hobonichi "cover on cover" they sell.

ETA: I didn't see your Amazon requirement, sorry! Here it is on Amazon as well. Welp, I can't read this morning, that's the A6 version on Amazon. Doh!