Khorium can be farmed anywhere in Outlands. It is a rarer ore to find though with a "chance to spawn instead of another ore" and even with my own custom full outlands path I normally would only get a little after a night of farming. The drop rate is something like 5% in comparison to the other ores in the area. If you only need a small amount to craft a few things then I would say just hit the AH and buy it when it is around. Other that that, Nagrand is supose to be the best place to farm it especially along the mountain ridges. Best of luck to you!