How can I redownload a book that I've already purchased but don't see it in my itunes?

If you are signed in with the same acconunt and they are still in your country's store then they should in the Purchased tab in the ibookstore in the iBooks app on your phone, and the Purchased under Quicklinks on the homepage of your computer's iTunes. If they are still in the store and they don't show then have you changed countries or are they hidden : (hiding and unhiding) ?