I have an idea.
Why not make a job where you have to be responsible for the transfer of guns to criminals? You would have to add a mechanism to force the person selling the gun mark up the price. It wouldn't hurt to maybe make the person selling the gun leave a clue if the deal takes too long, and you could mix it in with that sort of cinematic type of view you have planned for mugging.
Additionally, if possible, illegal gun deals should be a witness-based crime where if a cop sees you doing it, you become wanted.