I'm a teacher at a Callan school, so I can answer your questions from the inside. There is no Callan franchise. It isn't like the Berlitz or International House chain (for information on how to open your own Berlitz school, look here: http://www.berlitz.com/franchisingsupport.htm). In his directors manual (anyone can buy this from the school in London; it's no big secret), Callan says that he tried franchising the school, but found that it wasn't possible because it wasn't the materials that were most important, but how the materials were taught - and he couldn't ensure that it would be taught correctly in all those schools and couldn't set up a system to check that. So instead he simply makes his money by selling his teachers' books and students' books. Any school can use the Callan method, but they can't call themselves 'the Callan school'.
And by the way, there aren't any secrets in our teachers' books - they are just larger versions of the student's books. For the best results, the method has to be taught as it was intended to be taught and the school has to be very well organised to make sure that the teachers are doing their job properly and that the groups are moving forward at the right pace - not too fast, not too slow.
As lots of people have said on this site, the method works because: the material is systematically repeated and no time is wasted in the classroom.