If it is those it’s the wrong end of the market for me – they’re usually done by awnings folks and the like, best bet is to have a look at
British blind and shutter association
John Lewis do their homework but they don’t generally have exclusive distribution deals so may also be worth dropping sc a line to ask for a recommended supplier installer, there’s a good chance you’ll end up with the same folks as through JL but without the additional markup (and warranty etc that JL offer over and above).
If you’ve no luck that way pm me and I’ll have a look on Monday at who i deal with down there that might be able to help but most of my folk are interior designers in London (pays better and no getting your hands dirty, that’s for us filthy northerners)