Container Corps in Portland, OR makes some of the most awesome notebooks I have ever seen. Though I'm not sure how flat the pages sit. They really don't show that in their collection of ten photos. I may try building my own wood notebook sometime this spring/summer. I have some mahogany planks just sitting around waiting to be used for this very purpose.
64 leaves, 128 pages | 4" x 5.25" | $45
Available in:
Cherry, Oregon Bigleaf Maple, Western Juniper, Oregon White Oak
The following are currently sold out: Western Walnut, Beech, Madrone