There's always the local windscreen fitters...Auto Glass sourced and fitted me one within 48hrs, so I'm sure a small local firm could source one for you.
Perhaps try Bulli barn at Colchester, VW Downunder at Basildon or Harry Harpics at Rochford, sometimes they have spares for sale! Sorry don't have the phone numbers but they all have web sites.
Kool, I’m debating a road trip as a friend of mine wants one too, so think I might as well go c&c and get a heated one too