When I first started growing flax, I bought my flax-for-linen seeds from The Hermitage. They sell Marylin variety of seeds from the Netherlands, which is one of the main varieties for linen flax. The only problem I had was that the seed came coated in nasty chemicals meant to prohibit diseases that flax is prone to.
I didn't really like that idea, so I saved my seeds from one year's crop to plant the next year. This worked well, but I didn't produce quite enough seed last year to plant my regular amount. I searched for a source of fiber flax seed that was uncoated. It was hard to find, but I did find a source of uncoated Marylin flax seed. The original source of the seed is again the Netherlands, but the shop from which I bought the seed is in the U.K. The shop is Wild Fibres. Click HERE for the link to their flax seed page.
I have about 5 ounces of my own seed saved, plus 8 ounces from Wild Fibers. I'm very happy and can't wait for planting time. I usually plant 8 ounces, so I should have plenty for this year.