The reviewer of the Anne Bailey edited order book In The Saddle With The Texans: Day-by-Day with Parsons's Cavalry Brigade, 1862-1865 in the current issue of Blue & Gray notes that it is rare to see order books published. Perhaps the smaller scale just makes the project more doable (I can imagine the size of an Army of the Potomac order book), but the ones I have seen all relate to operations in the Trans-Mississippi. James McGhee has done some nice work with:
McGhee, James E. ed. GENERAL M. JEFF THOMPSON’S LETTER BOOK JULY 1861-JUNE 1862. Independence, MO: Two Trails Publishing, 2004. Illustrated, index, paperback.
McGhee, James E. LETTER AND ORDER BOOK, MISSOURI STATE GUARD 1861-1862. Independence, MO: Two Trails, 2001.
McGhee, James E., comp. VOICES OF THE SWAMP FOX BRIGADE: SUPPLEMENTAL LETTERS, ORDERS AND DOCUMENTS OF GENERAL M. JEFF THOMPSON’S COMMAND 1861-1862. Independence, MO: Blue and Grey Bookshop, 1999.
Researcher Carolyn Bartels has also compiled the following:
Bartels, Carolyn M., CONFEDERATE STATES ARMY TRANS-MISSISSIPPI ORDER BOOK 1862-1864 BRIGADIER GENERAL JOHN S. MARMADUKE. Independence, MO: Two Trails Publishing, 2000. Hardcover, 2 vols. in one.
These letter and order books are a good resource, and Two Trails Publishing and Camp Pope Bookshop have been printing and reprinting valuable Trans-Mississippi primary source materials for many years. Click on the above links for more information on these titles and more.