In 2368, the USS Enterprise-D arrived at Qualor II to investigate the fate of the Vulcan transport T'Pau, which had been sent to the depot but whose deflector array had somehow been found among the debris of a Ferengi cargo ship. It was discovered that arms smugglers had been stealing components from the depot by masquerading as the USS Tripoli, and that the Romulans had contracted them to steal the T'Pau as part of a plot to invade Vulcan. (TNG: "Unification I", "Unification II")
Background information Edit
According to the scripts for "Unification I" and "Unification II", the pronunciation for Qualor was "KWAY-lohr 2". 
According to the Star Trek: Star Charts, on page 61, the Qualor system's primary was a Class K star. It had a magnitude of +5, which was the same brightness as Sol. By 2378, Qualor II was a member of the Federation. This system was located in the Beta Quadrant.
Qualor II figures prominently in the PC game Klingon Honor Guard as one of the first locations explored by the player, in the role of an Honor Guard trainee. The Surplus Depot was not featured in the game, nor was the fact that Qualor II was a Federation world mentioned or made part of the game story. In the Klingon Honor Guard game, Qualor II was portrayed as a safe haven for pirates, criminals, and mercenaries similar to the island of Tortuga during the heyday of seagoing pirates on Earth.