Rob - you can get one here - http://www.masterautoglass.com/index.htm

These guys are a glass supplier only, don't do fitting, just sell glass, to both trade and public. Branches in Walthamstow (E17) and Park Royal (NW10)

Worth giving them a ring, I'd be almost positive that the Walthamstow branch will have them instock, and worth seeing what price. Also you can then ask them to recommend you a fitter, as they know all the local guys as they trot in and out day in day out.... Might be quick, and possibly cheaper that way.... Get your own glass, and ask for a fit only, or get a local guy to do it, as he'll no doubt get discount off the "street" price from Masters.....