All refills can be purchased from this website under Accessories (http://www.treeringpens.com/accessories/refill-cartridges.html). Also most office supply stores carry the standard size refills used in Tree Ring pens. Rollerball pens use 888 Int'l Standard Rollerball Refill, which is the most common rollerball refill shape in the world. Ballpoint pens use Parker style refill, which is the most common ballpoint refill. Fountain pens can use either the international size short or long refill cartridge.