Hi ^_^

You don't need anything specifically cels-related,
the most common type of "cel book" is really a 
scrapbook by Itoya (Art Profolios). These are 
cheap and quite ubiquitous at art stores. If you 
don't have access to a reasonably stocked art 
store, you can buy Itoya books from many on-line 
art-stores like Dick Blick (dickblick.com). There 
are other types of books/presentation 
cases/binders you can use as well. (More links are 
available at my cel supplies page, though I need to 
update this page over winter break.)