As this is a brand spanking new website there aren’t many resources yet, but here’s a few good ones to get you started;
Lawrence Art Supplies – great for printmaking supplies. Based in Brighton, but with a great online shop.
Intaglio Printmaker – one of the widest ranges of printmaking suppliers in the UK.
Dick Blick Art Materials – a vast array of art supplies available from this US based site including printmaking supplies.