There only seem to be two main suppliers of Guernsey 5-ply wool nowadays, Frangipani and Wendy’s. If you know of any others, please let us know.
Available online from http://www.guernseywool.co.uk/ or direct by mail order from “Lamana”, White Cross, Cury, Helston, Cornwall TR12 7BG. Comes in 500g cones, nice and even to knit, with hardly any knots. Wide range of colours. Extremely friendly mail order service.
Frangipani is also available from the Yarn Cafe at http://www.theyarncafe.com in 100g and 500g cones and balls; they also stock a variety of other, non-gansey related knitting supplies.
A traditional but limited range of colours (navy, cream, red, etc.). Slightly chunkier than Frangipani, comes in 100g balls so there are inevitably going to be joins in your gansey. I’m a fan of their navy, which has a nice sheen to it (as does Frangipani’s). It is widely available—put “wendy guernsey 5-ply” into a search engine to find stockists—or order online from the Love Knitting website.
British Breeds Yarns (formerly Creskeld)
[Does not seem to be currently available.]
This is the website of the Hebridean Isles Trading Company, operating from the beautiful Isle of Skye. After a disastrous fire in December 2013, the company moved from Colonsay to Skye. They offer a range of products, including their own Colonsay wool, fleeces, knitwear, books, and courses. Bed and breakfast accommodation is located nearby. I haven’t tried their wool yet, but it’s next on my list. (You can also follow what they’re up to on their blog.)
Finally, here are some other suppliers you might like to consider. I haven’t used them myself, but if you read the comments below you might find recommendations.
Flamborough Marine – They’ve been around since 1981 and their website says they are, “Your source for authentic hand-knitted Ganseys, Gansey Knitting Kits, Armor Lux pure cotton Breton shirts plus a range of quality, pure wool, traditional knitwear from Le Tricoteur (the original Guernsey sweater) and Armor Lux of France.” Well worth checking out. Their kits use Frangipani yarn. They are also the go-to place if you want a hand-knitted gansey made for you.
Bobbins of Whitby. Gansey kits (yarn and pattern) and gansey yarn in 1 kilo (2.5 lb) packs, in navy, atlantic blue, red and cream.