Or Ebay

Get most of my nuts, bolts and screws from there. UK based stores deliver in a couple of days.
Used to have a fabulous old school hardware store in Rushden when I first moved here - Peter Crisp - they had every type of metric/UNC/UNF/BA etc fitting in stock. Used to pop down with an assortment of old bolts and they could usually sort me out. Sadly now a Tesco Express.....