From about May through mid-October, you can check out some of the local farmer's markets. They are all over the city and also in the foothills. I am only aware of those on the south side of town and in the foothills and they include: Aspen Grove/Littleton, SW Plaza Mall (also Littleton), Highlands Ranch Town Center in Highlands Ranch, Cherry Creek in Denver, Pearl Street Mall in Boulder and for the foothills, both Evergreen and Conifer offer them. Each of these are on a designated day each week so you merely need to determine which one(s) you want to attend and search for days in which they are held in that area(s). I am sure there are more around town. I have only attended these. Try Googling "Farmers Markets Denver" or "Farmers Markets Colordao".
In the winter months, I think Sunflower Market, Vitamin Cottage/Natural Grocers, and Whole Foods are your best bets.
