I brought 6 quarter plate (3 1/4 x 4 1/4) holders on Ebay (new in the boxes, believe it or not), not realizing they were for glass plates, not film. I watched Ebay and finally found enough of the appropriate film sheaths. Just program the Ebay search engine and sit back and wait. Film sheaths are fairly common items on Ebay. The only size I've never been able to find is 3 1/4 x 5 1/2. I finally gave up and made myselt a set out of brass sheet metal.