Gloomy Etched Warbow  

 

This bow's item ID is sandwiched between others that are either of unknown origin or dropped during a special event. Some of the items allude that this event was between the Armies of Eldritch Collective and Meldrath the Malignant. Unfortunately I don't know when this event occurred and can't find any links to it. Here are the other items in the sandwich:
ID 69209: Clattering Bone Necklace [GM event]
ID 69208: Iron-Crafted Wand
ID 69207: Gloomy Etched Warbow
ID 69206: Dark Linked Chain Gloves
ID 69205: Steel-Lined Clockwork Vambraces
ID 69204: Flesh-Covered Earring of Unlife
ID 69203: Toxic Ring of Death

I think it's reasonable to conclude they were all dropped during that event and are no longer obtainable.