Where could I source genuine parts for a 1972 Ford Cortina GT?

Where could I source genuine parts for a 1972 Ford Cortina GT?

Do I need a genuine BMW windscreen replacement for a 5 Series?

I looked at non-manufacturer approved 5 Series at a BMW dealer. The car was nice apart from a two-inch crack in the front windscreen and worn brake pads (the seller said that it can last for another 6...