helmets come up fairly often but are getting rarer due to being converted to para spec as the shells are the same,anything above a size 7 is rarer but they do turn up at fairs,as has been mentioned soldier of fortune do breeches and standard bd blouses,boots are a problem particularly in larger sizes but did continue in use into the 70s so occasionally turn up,personally I just use bd trousers and dms boots as I don't fancy riding in hobnails. Dr macs also turn up quite often but weigh a ton,take a look at the wd motorcycle forum header picture at the moment to see what people are wearing and it maybe worth putting a wanted ad on there
Nigel