Go to USS's or Nav Beacons, and use a Cargo Scanner to scan traders.
Look to see if any of them are carrying any narcotics, and you can either use the Hatch Limpets to siphon the goods, or attack them and use sub targets to target their cargo hatch, in an attempt to break it.
A lot of NPC traders when under attack will usually drop their cargo, so they don't get killed. What you do with them after is up to you.
But note that if you do this, and attack clean ships, then you will gain a bounty and the feds will attack you.