Here are some link from Paul living in the UK.
Col-Erase Pencils: https://www.chromacolour.co.uk/prismacolor-col-erase-pencils-box-of-12.html#
They are both currently out of the black pencils, I was lucky enough to grab the last 2 verithin pencils; that said, it will be worth it for UK students to bookmark these websites and add the pencils to their wish lists so they will be notified when they restock.
I currently source my col-erase and in the future, unless restocked on UK sites will be sourcing my verithin pencils from the website below; Blick. Though this is a US seller, they ship to the UK. Orders typically arrive within 10 days with Fed Ex and are, at the moment, constantly in stock of both black col-erase and verithin pencils. Though import costs and shipping does apply here, on small orders the cost is not too bad and they are a reliable source.
Lastly for those looking for a reliable source of Strathmoore 400 series drawing paper in the UK, there is a sell on eBay that restocks 2 pads at a time regularly, I have used them a couple of times.
Strathmore 400 UK seller eBay: https://www.ebay.co.uk/itm/Pro-Art-Strathmore-Medium-Drawing-Spiral-Paper-Pad-11-x-14-inch-24-Sheets/392881537866