In this schematic the "Ybs67-5 Washer, Spring" is used most often.
Check out any of the thirty-six Swing Arm - Chain Case components enlisted.
Parts such as the Swing Arm - Chain Case: Ybs67-5 Washer, Spring, Washer, Spring, Protector, Chain, Shaft, Pivot are included in the Dt125 1979 Usa Swing Arm - Chain Case parts fiche.