The other place to get this done is anywhere that repairs motorbike leathers, they'll also have the heavy duty sewing machines necessary to do this sort of repair.

I notice you're in Sheffield. I know someone in Wakefield who is in the middle of setting herself up with all the right machinery to do this sort of work, she has 2 lovely antique cobblers sewing machines amongst others but I don't think she's up and running serving the general public yet. If you don't find somewhere better or closer in the next few days message me and I'll enquire for you.