This reminds me a bit of a lot of places in South-East Asia - There were town and territories that were Coke and others that were Pepsi... If you were in one then that's all that you could get.
Not sure of the mechanism behind it. For all I knew the government cola rights to each region up for auction.
That struck me about visiting China, too. I remember I got to Beijing, saw that literally everything was Coke and there was no Pepsi in sight, and thought "Damn, I oughtta buy Coca-cola stock." Then I got to Chongqing and Wuhan and everything was Pepsi, with not a Coke in sight.
When I worked in Mexico it was that way with beer. In northern Mexico every little pueblo was either all Tecate or all Modelo Especial. The residents would let you know their undying loyalty to the brand. "!Aqui somos tecateros!" The only exception I can think of was a remote mountain town loyal to marijuana instead. Locally grown, of course.
The most amusing thing I remember from the cold war, was the prevalance of pepsi in communist countries. That and the saying "coke for jews, pepsi for arabs" in the middle east...
Not sure of the mechanism behind it. For all I knew the government cola rights to each region up for auction.