Elddis window blind

I have a problem with the front centre window blind/fly screen in that the black cord came out of the cassette. I have pocked it back in and it has stayed in but the blind is very stif and difficult to operate. 

My caravan went in to a workshop yesterday for E&P to be fitted and i asked if it could be repaired. He said that it would probably be cheaper to replace it.

Does anyone know where i could order one? I can’t seem to find anything useful on the net - but I am an old idiot (so says my wife) all help appreciated.