Well, there are a couple of places I like to farm it on the alliance side. One is by killing the trolls in the Hinterlands. You can do a faction quest to improve your faction with the dwarves there at the same time. Or you could do the faction quest in the Felwood. The problem with this is that the quest is on one end of a very long zone and the furbogs (sp?) are on the other. It makes for time consuming quest turn ins. There are some of the mobs by the quest giver, but they are higher level.
I just found out with my orc that the dwarves of the Hinterlands, though they claim they are not part of the alliance, do no like the horde. So there’s no way to do that faction quest. Plus some of the griffons that won’t attack the alliance do attack the horde. So it’s a more dangerous zone. I guess I’ll be farming my mageweave in Felwood.
But any humanoid mobs in their 40s can drop the cloth, so you should have a fairly wide selection of farming spots.