When you help one of the big two factions in a dog fight that you run across randomly they’ll usually hail you and you can ask for ship parts (if they survived). Some vendors have them. Sometimes they drop in wreckage after destroying a ship. They’re fairly common when boarding a ship and looting the cargo hold.

The cargo hold is a small screen you can find in the cockpit that you can open like a storage. It’s not the captain’s locker.