M_Boats: Sheaves for masthead.

Does anyone know where to find replacement sheaves for the halyards in the masthead on a M17? I can’t seem to find any the right size on line. My boat is a 1976 M17 hull # 950. My mast is 21’-7” long. Gary Froeschner Columbia, MO msogggf@gmail.com Sent from Mail for Windows 10