Yes, local art supply stores are the best source.  (Office supply stores also occasionally carry some portfolios.) My local art supply stores have IA-12-11 for $12 and IA-12-14 for $22.  But, if you don't know where to find the portfolios, you can call Itoya and ask what retail dealers in your area carry the portfolios.  Detailed contact info is available on their web page or use the toll-free numbers.  Also, since Itoya sells a variety of things that art supply stores carry, the store might special order the portfolios for you (you do need the part number to be sure you get the right portfolio) if they don't carry the portfolios ordinarily. IA-12-11 works for most cels.  IA-12-14 is needed for some larger size cels and some cels with backgrounds.