2001 Ford Escort Brake Sensor

A Blue rubber stopper has dry rotted and fallen off. This stopper pushed the brake light sensor in so the brake lights do not constantly stay on and cause the battery to die. I have to disconnect the sensor when I leave the car to make sure it does not drain the battery. I have to plug it in to drive or else the gear shifter will not come out of Park. While driving, the brake lights constantly stay on. I know where the piece goes and can fix it. I am having a terrible time finding any automotive store that sells these rubber stopper pieces. Do you have any suggestions? Is there something else that can be used in lieu of the rubber piece?