The loop isn't to hold your foot in. It's so you can pull back the throttle in case of an emergency. Like a return spring breaking, or a motor mount, or something like that. It's a safety device.
They still show up at swap meets. But it might just be easier to go to the source and buy one. https://www.mooneyesusa.com/Store/index.php?cPath=188_23_160&osCsid=fd0b51859df4489c9dfedcc87e21b4e5 but as the photo you posted is in the Mooneyes add, oh well.