No trouble; manufacturing is one thing, distribution is another. Manufacturers would not have their own distribution centers.
Are you saying there would be no monopoly if for instance, if the only car a person could buy in the United States were a Ford Pinto as long as there were many different dealers selling Ford Pintos?
Don't you think that question is rather absurd Ted? If the only car allowed to be produced in the US was the Ford Pinto there would be a monopoly.