somebody on here above mentioned Unit sidecars here in the UK as suppliers of leading links. They do indeed make forks and the finish quality is good. They aren't as massively constructed as some and as they mount the caliper under the fork the front tends to rise when you brake. ]
There's another firm in the UK making leading links. Wasp sidecars who also make sidecars for off-road competition make road leading links. They are thicker and stronger. Wasp still don't have a website. My links are Wasps. They work well but need to be looked after as the finish is OK but not special.