There are a reasonable number of suppliers for your letterpress needs. This limited list is based on personal recommendations. Please contact me if you want to recommend a supplier or want to be added. The Letterpress Alive site provides a more comprehensive list of current suppliers.
Rollers
Rollers for common hand presses are available from a number of UK sources. Try Elli Evans, or Adana’s parent company — Caslon.
Printers' Suppliers: Paper, Inks, Card
Gemini Printers’ Supplies offer a comprehensive catalogue of different papers, and also supply letterpress inks and some other sundries.
Composing Room Stores
Quotes (from the Composing Room Stores)
Mr Julius Stafford-Baker, a great letterpress advocate and hands-on helper, has launched the first 21st Century store selling 19th Century equipment with his Composing Room Stores. You can order many of the requsites of the letterpress printer from him — furniture and leading, packing and quoins. You can also hire single words (properly ‘sorts’) from him in fancy types.