I found a cardboard carrier thing at a local Flax 
store in San Francisco for about $20.  All my 
oversized cels and sketches fit right in and the 
whole thing is tucked safely away in the closet.  
I haven't seen it online anywhere, but I did come 
across a couple of things that appear very 
similar to what I use.  Here are the links:

http://www.michaels.com/art/online/DisplayCraftCat
egory?cgnbr=CRAFTS-166

http://www.utrechtart.com/dsp_view_products.cfm?
classID=2212&subclassID=221210&brandname=National%
20Fiberstock

http://www.utrechtart.com/dsp_view_products.cfm?
classID=2215&subclassID=221510&brandname=National%
20Fiberstock