Barney Eaton has NOS retainers and nuts at a great price while supplies last. The dealer may still be able to order them also.
#25515544---Nut, snaps into the the metal cowl bracket.
#1637234---Retainer, (thumb screw).
After you snap the plastic nut into the metal cowl bracket, put a little white grease on the shaft of the thumb screw and push down slightly while turning it into the nut. It will keep the plastic from binding on itself and last another 20 years.