Any lookbook can be duplicated by selecting the checkbox in the right-hand corner of the book and clicking the Duplicate button. Arthur allows you to duplicate multiple lookbooks at the same time.
Note, after duplication, you may need to refresh the page to see the copied lookbook populate. The duplicate lookbook will automatically have the title "Copy of..." and the name of the original lookbook. You can changes those details in the editor by clicking on the new lookbook.