Hiya!!

First, I have to give credit to animiko who 
posted about this over at Anime Beta a few weeks 
ago.  You can buy Itoya presentation books in 
large sizes of 13x19" and 18x24" on Utrecht Art 
Supplies online site:
http://www.utrechtart.com 

I can't find a direct link to the Itoya products 
for the life of me, but you can get to them by 
doing a search on their site for "Itoya".  I 
just ordered a couple of 18x24" books from them 
a couple of weeks ago.  They happened to be on 
sale at that time for $22.99.  I don't know how 
often they have sales on such items, tho'.  I 
had no problems ordering them and got the books 
delivered ot me in less than a week.  I'm so 
excited to finally be able to properly store all 
my oversized pan cels. ^__^

Hope this helps!!
~Luna-Art >^.^<