If I sent you rigid plastic holders for them would you use them? Just sitting in a shoe box is not good for them as the Box is made of acidic cardboard. Also, curling, cracks and scuffing can occur. These are easily damaged.
I collect and deal in a wide range of antiques. Photos being a prime market for me ( and something I have collected for years ). I hate to think of them getting ruined. Will gladly send you rigid holders. I'm sure I can gather a bunch up.
Is that a scan of a negative that you flipped on photoshop? Great photo by the way!