There is a glaziers glass cleaner under various brands. The one I've
got is called 'Nilglas Nilco Glass Cleaner' in a polythene squirty
bottle. Made by Bluecol.
Very effective even on very dirty old glass but a bit fierce on
paintwork - a bit like sugar soap. Decorators paint that is, is ok on
car body work.
Try glazier, glass supplier or motor factor.

cheers

Jacob