There is a discussion in the comments section of this blog on sources of linen seed -- Joybilee Farm offers three varieties of linen seed for sale in 250 gram bags ($10 CND) plus shipping. A 250 gram bag will plant a 10 x 10 plot for fine fiber production or a 20 x 20 plot if you are looking for coarser fiber and want to produce more seed -- for oil extraction or to increase your seed supply.
But there are two other sources of fiber flax seed for sale in North America. One is Richter's seed in Ontario. Richter's sells "Evelin". I have grown this variety in my CND climate zone 3 and it performed well for me, producing 3 foot stalks in 100 days and adequate seed production to grow for a second season.
Another source, sent to me by Linda Heinrich, is the Landis Valley Museum, heritage seed project. They carry "Marylin" from Holland. Linda is the author of "The Magic of Linen" which is revised and due to be reissued this Spring. Looking forward to seeing the new edition with extensive revisions on the linen industry today.