There are larger-sized black-edged Ikea frames on sale right now. I use these for exchanging kids artwork in/out of as time goes on. Check out the link below if you are interested. I find them really handy for big or small works on paper as they have a nice large space around them which makes them look matted. I just use the white sheet inside the frame, turn it around, pop a few pieces of removable tape on the art and put the artwork inside.

http://www.ikea.com/ca/en/catalog/products/70167464/