2 master cylinders. They are on the pilot's rudder pedals. The pilot and co-pilots rudder pedals are mechanically linked so that pressing either of the co-pilot's rudder pedals moves the pilot's rudder pedals and vice versa. In either case, moving the rudder pedals actuates the master cylinder for that brake line.
The POH is specific in its wording. It does not say, "a master cylinder attached to each of the pilot's and co-pilots rudder pedals."
Some models do not have co-pilot's toe-brakes.
To quote the maintenance manual:
"5-59. DESCRIPTION. The brake master cylinders, located immediately forward of the pilot's rudder pedals, are actuated by applying pressure at the top of the rudder pedals. A small reservoir is incorporated into each master cylinder for the fluid supply. When dual brakes are installed, mechanical linkage permits the copilot pedals to operate the cylinders."