Yes, it is rare. If you want to find it, go to the forest near the second Gym's city. There should be an Haunted Chateau if you look properly. Inside it, go to the top floor and in one of the rooms should be a TV. Press A in front of it and you should be in a battle with Rotom. By the way, if it doesn't work, it's because I think you need to go there in the evening (after 6:00pm). Hope I helped!
you are right I've got one