I have a somewhat opposite problem. I have size 5/5.5 (US) feet and big (read: adult size) calves, and short legs. I had a heck of a time finding nice paddock boots and currently show unrecognized so the paddock boots/chaps work but next year I plan to go recognized eventing and throw in some dressage shows and need tall boots. I feel like I’m going to have to shell out money for custom boots.
When I was younger I could find off the rack to fit me but when I was a teenager my calves were a lot smaller. I can theoretically find my foot size in children’s sizes but the calf width is prohibitive.