I made this Runecloth Farming guide to help out players who want to farm the cloths instead of buying them from the Auction House. I decided to search for places with high density of mobs which I can kill and drop [Runecloth]. I traveled around Azeroth, and after a while I made a list of places.
Hellfire Ramparts - instance
Level 80 is recommended to farm at Ramparts, but you should be at least level 70.
The best thing about Ramparts is that once you cleared the instance, you don't have to run all the way back. You can just jump down and go outside. This saves a lot of time and makes this place an excellent farming location. However, you can only do 10 instance runs in an hour, this means if you are clearing this place under 6 minutes, you will have to wait a bit.
This is Normal Hellfire Ramparts, not Heroic.
After you cleared the instance, go outside and reset it by right clicking over your own portrait then click the "Reset all instance" button. This restarts the whole instance and all mobs will be back.
If your level is not high enough to solo Hellfire Ramparts, killing Twilight Cultists in Silithus is the best place to farm Runecloth. By the time you cycle back to the first camp, every mob will respawn..
Another great place to farm Runecloth is in Blasted Lands. Drowned Gilnean Merchant and other humanoids around this area drop a decent amount of Runecloth. I must mention that the drop rate compared to Hellfire Ramparts is horrible, if you can solo Ramparts you should go there.
Visit my Netherweave Cloth farming page when you have enough Runecloth.