Storage Envelopes for 5"x5" prints

I store my 5x5" prints in white window envelopes. These are the kind of envelopes you get when you take your film to be processed at a photo store. Had a supply, but the photo processor is no longer in business. They are white envelopes 5 1/2" high and 7 1/2" wide. They can easily hold 12 5X5 prints. The window on the envelope is 5 3/4 by 4". There is no printing on the envelopes, so I can not trace them. I then store the prints in a box. These are just my proof prints. Any suggestion where I might find these or other storage "envelopes" for 5x5 prints. Thanking you in advance.