Here it is: EECO Limited - The Exhaust Ejector Company Ltd., Wade House Road, Shelf, Halifax, HX3 7PE Tel: 01274 679524. We had a large front window replaced by them a couple of years ago.
Also have a look at, http://www.miriad-products.com/section.php?xSec=102&xPage=1&jssCart=8ae7012abc91ee338bb621d41aa49a2b
They are the sole importers of most caravan windows, they arn't cheap.