In Gendarran Fields is a centaur camp at The Blood Fields. At my marker on the screen is a Supply Cart. To the west where my walked path ends is another. Each contain between 3 and 6 random common crafting materials.
You can actually run between the two without agroing ANY centaur and by the time you've run from one to another they're usually respawned or are about to. Here's an inventory of my farm earlier.
Time spent farming: 15 Minutes
2 Lump of Tin
15 Wool Scraps
9 Spools of Wool Thread
10 Thin Leather Sections.
I know it isn't much but 61 Mats in 15 minutes is NOT BAD . At Level 27 the farm is EASY even if you accidently grab a Centaur or Two. Good LUCK and happy farm