Hi,
sorry to hear of the breakage. A firm that can make you a replacement window from your old damaged one or from patterns held in stock is,
www.eeco-ltd.com
Have not used them but they seem to be a call of last resort if you cannot pick one up elsewhere.
On other forums that I visit, breakers and parts stockists crop up regularly, can't recall names off-hand, if I come across them I will try and post them here.
The sites that I see such info on are;
www.motorhomefacts.com and
www.autosleeper-ownersforum.com
All the best
Davy