Fruil Model makes tracks for the Churchhill and Centurion but not for the Chieftain. ModelKasten makes tracks for those 2 as well, but not for the Chieftain. I am not one for British Armor, but even though the Chieftain tracks are similar in design as the Churchhill, I believe the Chieftain had rubber pads on the tracks.
They make resin track links. I am not sure if they make the ones that you are looking for though. They also have lots of conversions for the Chieftain that you may want to check out. I think you can order directly from them, or you can order through Great Models. Good luck in your search.