[link|https://www.reddit.com/r/logitech/comments/y8to77/mx_keys_rubber_replacement_feet/|According to Redditors|new_window=true], there are no replacement parts for the rubber feets, nor official nor third-party. Quote a solution (u/Dr_Artiick):
[quote|format=featured]Having a similar problem myself, basically one of the feet started to peel off. Your best solution is just to buy Silicone or Rubber feet from amazon and just "adapting" them yourself with a box cutter or razorblade. You can find 4x, 6x or 8x packs in different lengths or just one continuous strip. Will they be a perfect fit or will they be a mirror copy of the originals? No, they most likely never will be. Will they work just about the same and will they cover screw holes preventing dust and what not going in there? Absolutely, you'll be more than fine.[br]
Hopefully this helps ya, Cheers!
PS: By "adapting" I mean just trimming them lenght and/or width wise. Just cut in straight lines using the straigth edge of the blade itself as a guide and it's a super easy job. You can also replicate the original curved shape at the edges, but that's just tideous and time wasted doing a pain the arse job... Since the feet are at the bottom and you basically never see them.[/quote]