I farmed the black dragonscales from the Black Wyrmkin, Black Dragonspawn, and Searing Drakes in Burning Steppes. Drop rate wasn't too bad, took me about 5 hours to get 45 scales. You'll also get a mix of Worn Dragonscales (which I made into a Dragonscale Breastplate, and sold for 18g), Rugged/Thick Leather, and Thick/Rugged Hides. You'll have to go to an enchanter for the Enchanted Leather bit but as it's a learned recipe, not a dropped one, they are usually pretty fair about doing combines for free.
Took me 2 days to finally find someone to do the combine for my shoulders. One person wanted to charge 15g for a 30 sec combine. I didn't feel it was fair as I was providing all raw materials plus 5 extra black scales and 10 extra worn scales, plus some spare rugged leather. Good luck with your farming.
BTW, putting these on jumped my DPS roughly 3 points.