Here are the suppliers that I have used who have interesting seeds and plants for sale (in no particular order):
Incredible Vegetables – Heritage & perennial vegetable plants & seeds, plus Andean tubers
Incredible Vegetables is an experimental vegetable growing project and fledgling perennial vegetable nursery selling perennial vegetable plants and seeds in Ashburton, Devon,UK, set up by Mandy Barber and Julien Skinner. They grow unusual, heritage and perennial varieties of vegetables and herbs, Andean tubers, edible flowers and vegetables from around the world in a polyculture type growing space with lots of annuals, perennials and beneficial plants happily growing alongside each other.
They have a small selection for sale at present (January 2016) but given their enthusiasm I am sure this will quickly expand. I had very speedy service indeed.
Backyard Larder – set up by Alison Tindale, sells an interesting and ever expanding range of perennial vegetables and has a very informative blog.
Pennard Plants – heritage and heirloom seeds.
Edulis – growers of rare plants. Based in Berkshire in a walled garden Edulis specialise in growing rare plants and have a good range of perennial vegetables.
The Real Seed Company. Based in Wales they raise their own rare and heritage seeds, conduct trials of new varieties and breed their own. In their own words “out aim is simple: to assemble the best collection of really reliable, tasty and interesting non-hybrid vegetables for the home gardener, allotment grower or smallholder. They also encourage gardeners to save their own seeds and give lots of information about how to do this.
B and T World Seeds – if there is anything you cannot source try this French based site. They have an enormous range!
Nursery of Eric Deloulay based in France who also supplies Daubenton’s kale
The Scottish Forest Garden – a wide range of home grown seeds and a supremely interesting blog about this particular forest garden as well.