Depends on what you mean by “how important”. But in general, I am confident that while new guns, especially new unregistered guns, are useful to organized crime, and enable violence that would be harder without them, they are mainly just practical details that affect efficiency, risk and profits somewhat. They are not “important” in the sense that they are essential, and they are also very very far away from being scarce. As for your last question, it would be possible to get much information about guns in organized crime, but it is a complex subject and the questions you have may not already be neatly wrapped up in accurate unbiased articles that are framed in ways that are directly relevant to your questions.