If you can't find replacements, the mast fitting should turn over so the top bit becomes the bottom. The smaller bit won't be as easy to fudge, a couple of stainless washers and sacraficial PTFE discs was what I was thinking of using on this Jeanneau gooseneck:
Looks the same as the Kemp / Selden on the Sigma 33, if so here are the part numbers. from Selden
Goose neck fitting (boom bracket) 508-040
Toggle 528-015
edit If you zoom in on the togglein your photo I think you can make out the last 3 digits of the part number -015
I always though that a gooseneck fitting should allow for the boom to roll as well as rise and fall and swing sideways. This does not seem possible and I wonder if that is part of the cause of wear. ie the mainsail when you tack or gybe will tend to pull the top of the boom to one side or the other. The main sheet attachment doing the same thing. Still if it has lasted for 30 years can't be too much wrong with waht you have.
As said a boat on a mooring always moves and I have taken to dropping the boom onto the cabin top to keep it still so minimising wear of gooseneck and traveller. olewill