Hello Dave, being in an area where canal boating is dominant rather than Broads type, I would suggest you ask this question on either or both of these web forums. There is more knowledge that may help with that area of the country.
Where there is also a page called Tow Path Trader. You should find plenty of adverts for canopy makers but do seek some opinion of the individual companies either locally or online.
I had a quote from Nauticover for a new Canopy. They sent me samples of the various material options available. I still haven't got round to renewing the awning.