Try speaking to Townfields they might have a repair service that could do it for you.
There is a specialist shoe and boot maker in Tardebigge, near Redditch but I don't know the name of them. I can find it if you want me to, I drive past most days.
Kenilworth Cobblers did mine a couple of weeks ago - brilliant service! I had them back in a couple of days and the zips are really good quality. 01926 852057