Seals for secondary drive

No, a belt pulley or a chain sprocket do not have seals. And sealing rings for O-ring or X-ring chains are not available to buy individually. But the famous Duo-Seal sprocket nut for four-speed Big Twins 1970-1984, which seals with an O-ring against the sprocket itself and a shaft seal against the main shaft, needs new seals from time to time. And you can find them here.