I would like to open a custom shoe store called Solemates, and all it would do is build shoes to replace a shoe that is missing from the pair.
It turns out there is already a shoe store in Chicago by this name, but I bet they sell pairs. How common.
Perhaps if this takes off, we could also branch out into making matches to missing socks and gloves, or missing game pieces or playing cards, to recomplete the sets. I just need to get my hands on a 3D printer.