I suspect this is one of those things you are just going to have to "watch" on Ebay for a set to pop up. Good hunting. It's likely that this was a stock rubber foot rather than a custom Leica item (but with Leica you can never be sure) and available on some European hardware site. They are completely different from the ones on the baseboard of my Durst.
Just look that the height is correct so the metal plate on the bottom of the baseboard and the screw in the center of the column doesn't touch the table. There's nothing special about those feet (that I am aware of). I've used this kind on the Ic baseboard with no problems.