The Spring Pinion is the cheapest item from this partsfiche.
In this schematic the "Pin, Shift Fork" is used most often.
Parts such as the E-16 Shift Drum Shift Fork Kick Spindle: Spring,return, Pin,gear Shift, Stopper,shiftdrum, Drum Gear Shift are included in the Cb500k2 General Export E-16 Shift Drum Shift Fork Kick Spindle parts fiche.