Recently at "do" I was alongside a Children's Fun Bus. The guy who owned and ran it said that he also made canvas and heavy duty covers and such. I mentioned Punch fit-up covers and asked if he would make up own fabrics. He said yes, he'd do any kind of heavy duty fabric work.
He gave me his card and I said I'd mention it on here.
He's called "Atul Covers", is in the Wrexham area I think, and his phone number is 01745 870122
Anyone in the North West seeking such a service might like to get in touch.