A bidirectional ribbon supply system for a printer includes: a shaft supported by a frame of the printer, the shaft to rotate about an axis; a pulley affixed to the shaft; and a bias member coupled between the frame and the pulley to apply a force to the pulley in either of a first or second direction responsive to rotation of the pulley in the other of the first or second direction, wherein rotation of a spindle supported on the shaft in the first direction dispenses inside-coated ribbon toward a printhead, and rotation of the spindle in the second direction dispenses outside-coated ribbon toward the printhead.