Wouldnt bother bro! Only thing that has lasted in Denver as far as supp stores is GNC and I dont know how they stay open. No one is EVER in there. Max Muscle has opened in 3 locations around me only to close in a few months each time. One on One Nutrition was directly next door to one of the most busy 24 hour fitnesses around and they shut down in a just over a year or so? You may be able to get an edge in Boulder or DTC but otherwise, fuggetaboutit. You would have to sell products at prices close to that of DPS and BBing.com to attract enough business. Doing promotions work would not be a bad idea either. Get in with the local gyms like Mahaneys and all the little gyms popping up all around here. They typically do not have supp sales at them and the trainers would like to send them to a place with everything they may need instead of GNC. Even the World and Powerhouse gyms shut down to make room for "mini gyms" that offer no more than cardio and machines. Not really a supp happy area.
Hope this helps!