Had my perspex curved in Leeds by a firm who specialise in plastics but I had the old ones as a pattern. Littleport Boat Haven (LBH) might be worth a look?
I saw some posts on ribnet about your custom windscreens.
I wonder if you are able, and willing to assist me with a windscreen for an old Humber 530 that I'm doing up. The standard Humber windscreens are quite industrial looking.