A good while ago now I ordered from Namrick about £60 of M5 A2 stainless steel Allen-socketed machine screws in various kinds and lengths - cap head, button head and countersunk, mostly 30mm and 40mm, plus Nylok nuts to match. What I wish I'd done was buy stainless steel M5 washers rather than 1000 zinc-plated, because those still inevitably rust.
Remember, if you're screwing small steel things into big aluminium components, don't apply copper grease to the threads as your anti-seize measure, but use something like MS grease instead. Copper grease will react with the aluminium and corrode to permanently retain your delicate derailleur adjuster barrel. If it's steel into steel, copper grease is fine. For the same chemistry, don't use small aluminium machine screws in big steel components, because they will also corrode beautifully.