I purchase raw flax from a spinning store on the web.
I have backed 2 bows with it - a white oak longbow at 50# and a red oak at 40#. It is a major pain in the a$$ to work with. Used TB3 to glue it down and 99 cent store combs to smooth it out ... used a lot of fiber because I was never happy with how they laid out on the backs of the bows, so I would strip them all off and start over again. Hickory backing is the best choice for me.
Grandpa Bill