Ooo, take a look at paperbacknote.com for a whole selection of blank notebooks with covers from second hand paper back books. There are some truly great finds that will keep your notes spectacularly undercover (so to speak).
“Our notebooks are made with second hand paper-back book covers containing stitch-bound blank sheets, allowing the book to open flat. Each book is hand assembled, with rounded corners, and an embossed logo on the back cover. The size is approximately 11cm x 18xcm x 1.2cm with 120-140 pages.” -paperbacknote.com