The Mature Blue Dragon Sinew is the tendon of dragonkin from the blue dragonflight. It could be taken from Azuregos in Azshara and dragonkin in Winterspring.
"Mature Blue Dragon Sinew Unique Requires Level 60 Item Level 71" Comment by picklemonkey Why, oh why, is this still selling on the AH when (to my knowledge) you can't complete the quest anymore. So strange. Comment by As the quest can Sibew longer be completed, I'm assuming this item is no longer obtainable. Comment by Acccattone Sold one Mature Blue Dragon Sinew 50k on Silvermoon a week ago, so yes - they.