The local regular ol' fabric stores have the sticky back form of the low-hook Velcro, called "industrial strength", but I've gotten the non-sticky form at the local outdoor fabrics wholesaler, Rose City Textiles, and I know a bracemaker that's using the non-sticky back form. I suspect it's going to be available first in the places that sell overage to small manufacturers and consumers, and then maybe in the outdoor fabrics store. If I've got UK shops straight in my head, I suspect you'll see it first at Croft Mill or Pennine Outdoors, rather than the shops in High Street.
Kay