Are you talking about the piece of rubber gasket that is fixed on the doors to avoid the door hitting something while opening?
If so, by default, these used to come with the car when they transport it to the dealer. Some SAs will just remove it and throw it away. When I wanted a one, they just took it from a new car from the stockyard and fixed it to my car.
1st snap is the samples of door beadings (the rubber ones running over the door boundary)
BTW, if you are planning to use them to avoid your door hitting walls / adjacent vehicles, it will not be very effective. These pieces are prone to fall down in no matter of time.