There are larger portfolios out there.  I have a
Prat Presentation Case.  I suggest looking at the
selection at dickblick.com (or other art stores)
or even better, at local art store where you can
get a feel for size and weight right there.  There
are a lot of potential 'cel books' out there.  Be
careful though, some cases don't have pages in
them.  You might want to try looking at albums and
scrap books as well as presentation cases and
portfolios.  As a last resort, you can always
create something make-shift too ^_^.  Hope this helps!

Keys