Somebody (possibly the proprietor) recently submitted a link in the Archive/Services to EKP Supplies UK Screw Manufacturer and Stockist. Looks like a good and reasonably-priced online source of those harder to find metal fasteners we're always hunting down:
Maker of fittings and fixtures based in U.K. primarily for the hobbyist market. Making screws, nuts, bolts, washers, grommets etc of many old standards like BA, UNC etc. Very cheap and quick delivery, ordered lots of domed head bolts for award cards. Made in Steel and Brass. Also other engineering items.