It is expensive to buy flax ready for spinning into yarn. If you want to grow or buy flax straw and process the fibre yourself so it is ready to spin, it's difficult and expensive to buy flax tools to do that. To spin flax into yarn, it works best to use specialized tools.
This is why for so many years I have put off getting into flax, other than weaving a bit with commercially-spun linen yarn, despite loving linen textiles so very, very much.
Flax fibre comes from the tall, unbranched stalk of a flax plant. The plant grows from seeds bred to produce fibre and the seeds are planted closely together to prevent the plants from producing branches. The product line flax is fibre that is as long or nearly as long as the original flax plant stem. It is not chopped up. The best linen fabric is from line flax. To process flax plants to make fibre from them that is ready to spin into yarn, you have to ret the flax, break it, scutch it, and hackle it. Respectively, this partially decomposes the stalks, breaks away the outer material, and combs the fibers to align them and eliminate short fibers.
I found flax hackles for sale on the Windham Woolwork website. A set of coarse, medium, and fine hackles would cost hundreds of dollars, and I couldn't find any information on the site about whether they ship from the U.K. to the U.S. or not. The only other place I could find that sells new flax hackles is TelTechArts on Etsy. Unfortunately TelTechArts hackles only come in one coarseness, not as a set. The Woolery lists one flax hackle but it is out of stock. The Woolgatherers website sells plans to make flax hackles as well as plans for a flax break and scutching board. Cindy Conner, author of Homegrown Flax and Cotton, has a description on her blog about how she started with an antique hackle and rounded out her set by making a couple of other flax hackles. I remember a long time ago reading a statement from Indigo Hound explaining that they did not make and sell flax hackles because they could not do it more cheaply than people could buy antique hackles.
Then there's the labour. According to the website Flaxland, "It will take around a day to break, scutch and hackle 1 kilo of long line fibre and 1 kilo of tow from retted flax stems, using hand tools." A kilogram, 1,000 g, is 2.2 pounds. So in other words, in a day, not including the retting process, you could process by hand as much flax as you could buy already processed for $220 USD, assuming $25 for a 4 ounce (112 g) flax strick. However, you would have to build up the grip strength needed to process flax all day. I tried processing a small bundle of flax fibers once, as much as I could hold in my hand, and my hand got very sore.
First, of course, you'd have to get unretted flax straw. I don't know of anywhere local that sells it. The one place I do know of that sells it, Landis Valley museum, has a website that puts my computer's security feature on high alert so I wasn't able to check the current price. The museum also sells the right kind of seed. It's no wonder that Cindy grows her own flax and saves her own seeds. To grow flax you need land or access to land, again costly. Elsie Davenport's book Your Handspinning states that the soil needs to be sandy. Here is central Virginia we have clay, so you'd probably want to amend the soil. I assume the soil needs to be somewhat enriched. Cindy has a DVD for that, Cover Crops and Compost Crops In Your Garden.
I should point out that for $27, slightly more than the cost of a flax strick, The Woolery sells a 4.4 ounce (123 g) cone of commercially spun linen yarn that comes from line flax. It is comparable in quality to a flax strick. My conclusion is that you have to really want to spin flax to pay for flax stricks.
I have seen handspinners spin yarn countless times with wool and sometimes with cotton, angora, mohair, alpaca, and blends that contain silk. But I've seen them spin flax less than a dozen times. It's rarely done and from what I can see the skill is not being passed on, save for at the occasional class at places like The Folk School. My guild has wool combs, spinning wheels (one with a distaff), and a floor loom for rent but nothing for processing flax. The tools, equipment, and supplies for spinning flax are costly and hard to obtain and I think that's a reason why handspinners don't get into flax. And since they don't get into flax, that means the market is small and that in turn means there is little incentive for businesses to cater to the market. I think it's a cycle.
It is easier to spin flax if you have special equipment, such as a distaff and a spindle meant for flax or a spinning wheel meant for flax. Examples of spindles meant for flax are the Medieval spindle shafts and whorls from NiddyNoddyUK on Etsy, but if you order a spindle shaft with spiral tip there, ask for it to be counterclockwise or S because flax is spun counterclockwise due to its physical properties. I've heard that Turkish spindles are good for spinning flax, and I'm told the best Turkish spindles are from Jenkins. A distaff holds the flax arranged so it can be drafted easily. Distaffs are hard to find for sale. Few handspinners I know have this stuff. Cotton takes special equipment too, yet I know handspinners that own tahklis and charkhas. Nice and expensive charkhas too, from Bosworth Spindles.
It is rare for a handweaver or knitter to use linen yarn to create a linen towel or a linen sweater. I can't remember the last time I saw any finished objects in linen in show and tell at a guild meeting or in a festival display. Whatever it was, it was probably a woven garment of Cindy's. I'll see on Ravelry garments knitted with a commercial yarn containing a small percentage of linen. Now, there are some handspinners that tell me that they will still spin yarn they have no use for, but you can see why it might inhibit most handspinners.