London Graphic Centre
They’ve been going since 1970-something and specialise in ‘material to the art and design community’ and more! Aimed more for designers, this still provides a hefty amount in typical art supplies too.
Now their prices aren’t cheap, but they are fantastic for whatever you may want; the bits and pieces you can’t find elsewhere.
They also have more than one store in London; their flagship and biggest is in Covent Garden and also Goodge Street and Barbican.
Have a browse online to see just how much they offer and in things you may never heard of.