Google for on-line or contact a local company that erects polytunnels by checking in local newspaper or yellow pages.

There is a company not that far from you. It's five star, They do supply polyt, and may even know people who erect them for you.
Is your frame no good? is non of it salvagable. As five star also sell just the polythenes.

http://www.polytunnels.me.uk/

will send you a PM.