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.
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.
Chiltern Seeds are based in Cumbria and sell a very wide selection of both vegetables and wild and cultivated flowers sourced from round the world. Their catalogues are informative and well presented. They have a number of perennial vegetables
Tuckers Seeds are an old established seed merchant and maltsters based in the West Country. Amongst their wide range of vegetable seeds are some interesting perennials including 9 star perennial broccoli and Jerusalem artichokes.
B and T World Seeds – if there is anything you cannot source try this French based site. They have an enormous range!
Plantes et Jardins are a French company and amongst other things supply Daubenton’s kale.
Nursery of Eric Deloulay based in France who also supplies Daubenton’s kale