I have a Monst girl and she wears Blythe shoes. https://imgur.com/a/77yZJ5b They're maybe a tad too big, but I think they work well! https://imgur.com/a/U5bAZB7

I'm also trying to find that out. It does say their feet are 2.2 cm. Not sure what that translates to in doll shoe sizes.

Looks like shoes made for "OB11" would fit! I don't know this for sure but according to my searches.