Check your local craft and art supply stores, as they will probably stock broad nibs. It is sometimes possible to find calligraphy sets in stationary shops - I've seen sets in WH Smiths from time to time.
It's also worth checking e-bay, as some people sell off unwanted pens, nibs, and sets.
Manuscript Pen Ltd. stock calligraphy equipment; the brochure is availible from the website as a .pdf download.
Parker and Sheaffer also make calligraphy sets. They tend to turn up regularly on e-bay as unwanted gifts.
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