There are over 200 brands of Root Beer in Colorado. And I have drank most of them. There is a chain store called Rocket Fizz that has shown up recently. There is one in Ft Collins, Boulder and Estes Park. They have over 50 different brands of Root Beer as well as other sodas.
ACE Hardware has also started carrying Root Beer, mostly Frostie.
I have been asked by a few people where to buy Virgil's Root Beer. It is one of the better brands. The place I buy mine is Natural Grocers.
My favorite Root Beer changes throughout the year. One of the better ones I like is Tommyknockers. It is brewed in Idaho Springs, Colorado.