The centaurs in southern Desolace are pretty good at dropping mixed silk/mageweave (lvl 34-38). For purely mageweave, I like the Dark Iron dwarves in the caves in Searing Gorge but they're a little higher (lvl 43-48?) and I can also occasionally find Dark Iron Ore to mine there for Thorium Brotherhood rep. The furbolgs in southern Felwood also have a high drop rate of mageweave, and help farm up your Timbermaw rep. At level 44, you may be a little on the low edge, but as a warlock you can probably solo pretty well.
Definitely Scarlet Monastery for silk, but the ogres in the Alterac Mountains are also good.