The trimmed spools that J&C sell do work in the Medalist. I usually rolled my own though. I know it's not much of a chore, but I would still prefer to use any 120 right out of the box.
You do have to use a 620 takeup spool though. The holes/notches in the ends of the 120 spools are bigger than in the 620 spools and the winding crank won't grab properly.