M_Boats: Spreader Ends

My '84 Monty has plastic caps at the ends of the spreaders with plastic pieces that screw onto those caps to hold the shrouds in place. The cap and screw-on piece both have a groove for the wire. Are replacement parts available? If not, would rubber spreader-boots be sufficient to hold the shrouds? I know the spreader boots are designed to prevent sail chafe, which would suggest they're probably not sufficient for the dual function of holding the shrouds.