Don't try to ask that in Christania you might end up in trouble or atleast get an angry answer. Drugs aren't sold on the side streets either. They are sold everywhere outside christania like by the central station. Take if from someone who spend every day there. Got a friend who was drunk and was doing cocaine in one of the establishments there and when it was discovered he got beaten up and banned from the place.
I assume those guys in the know was talking about the side streets outside Christiania? While drug trade can happen everywhere it is actually pretty controlled in Christiania because it is a tight-knit community which is self-policing. If you want to buy drugs (besides Hash) in Copenhagen you go to the sketchy areas behind the Central Station.