The biggest problem with growing flax for spinning, is finding the right seed.
The flax plant we use for making yarn is the same plant as we use for flax seed, linseed, linseed oil, animal feed, and several other applications that may surprise you. That said, different cultivars or varieties of flax are better for some things than for others. Some flax has a short, bushy stem. This is great if you want a lot of flowers or seeds, but not so awesome if you are making yarn. Flax for spinning, has a single stem, about 2 to 4 feet tall, with very few branches and blossoms. Some of how the plant grows can be influenced by the gardener. For example if we want taller, longer stems, we plant the seeds closer together. For the most part, the characteristics of different flax varieties have been selected for generations based on what sort of use the people wanted.
Here are some sources of fibre flax seed or seed that may be able to produce fibre for spinning, that I've found over the years. Some of these ship to Canada only, others to the US, others to lots of different places.
In the past, they sell seeds by donation to help fund their public demonstrations. The seed is organically grown in Victoria, BC (well, Saanich actually). I don't know what their current seed selling policy is, but it's worth a shot asking them if you are interested in growing your own flax.
Variety: Electra - developed by Biolin Research, Alberta
I've grown this two years in a row and am impressed with how it preforms, both in the garden and in processing into linen. I've experimented a little bit with planting timing, planting as early as January and as late as the end of May. The late Feb plantings did best for me.
They also carry a few other heritage varieties of flax that look promising for fibre production. Just because they don't say these are for making linen, dosen't mean they can't be used for it. All flax has fibre hidden in it's stem, perhaps it just needs the right conditions to make it useable.
... also has fibre flax from time to time.
At the moment of writing, they have Evelin Fibre flax in stock, but Reginia Fibre Flax is out of stock. They also have a listing called 'flax' which may also be useful for fibre making. I can't tell how tall it is from the description, but if one had the room, it would be worth trying.
Wild Fibres UK also has flaxseed, however I don't know if they ship overseas or not.
Flax for Sale is a place in the US that sells seeds as well as fibre for spinning. They don't mention if they ship internationally.
Woolgatherers sells Marilyn Flax seed which originates from Holland.
Know of any other sources of flaxseed? Please let me know in the comments section.
Other thoughts about flax seed.Flax takes about 120 days to grow from seed to harvest, The first half of that time it needs plenty of moisture and can easily withstand frost. For the last 60 days, it enjoys dry weather. For that reason, I like to plant mine very early in the year. I always keep back a bit of seed just in case there is an especially heavy frost, but so far, I've not needed to reseed.
I've seen several mention of flax being planted as an over-winter crop. Planted in the fall, like grain or fava beans, it grows a little, then goes dormant until late winter when it takes off at an accelerated rate. This seems to be traditional for the Alps and Himalayas.
The flax flower is self fertile, having both male and female parts. It is considered an inbreeder, with an observed pollination by insect at 3% (that's less than tomatoes). When saving seeds, the recommended isolation distance between varieties is 0 - zero what, it dosen't say. (Breed Your own Vegetables Varieties by Carol Deppe)
It doesn't say if that information is for modern agriculture or an organic setting that has fewer pesticides and more bugs. I've noticed when I grow flax at home that pollinators seems quite fond of my flax flowers. So, it is possible that flax is more willing to promiscuously pollinated than previously thought.
Given these thoughts, flax may not be the best plant in the world to use for landrace gardening, but it has some potential. I hope this year to experiment with different types of flax and different planting times.