I agree that he is a white leghorn cockerel. He could have a leg bone deformity that is getting worse with age. Does he limp on one leg or turn it out? Could you get some pictures of him standing from the front and back without any leg hobbles? A short video of him walking uploaded to YouTube or Vimeo with a link here could be very helpful. Does he hold his head up normally most of the time?
I would try to get his leg problem figured out before getting new chickens. For example, if he were showing signs of Mareks or a deformity that might require culling, then there could be a possibility of a disease spreading, or having chickens without a rooster.