The Volnar colony was a colony existing as of 2371.
According to Tom Paris, there was a shop at the Volnar colony that sold a dozen Lobi crystals of assorted shapes for one lek. (VOY: "Caretaker")
Background information Edit
This colony was only mentioned in dialogue.
Taking into account that Paris numbered the price in lek and not in latinum or Federation credits, it can likely be assumed that the colony was Cardassian.
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), there was a star system named Volnar, in which this colony might possibly have been located, in the Alpha Quadrant. The system's primary was a G-class star. In the late 24th century, it was a Bajoran system.
According to the Star Trek Encyclopedia (3rd ed., p. 548), the Volnar colony was a settlement in the Bajor sector.
According to StarTrek.com, the Volnar colony was located near the Deep Space 9-Bajoran area.