RNG sucks, but it's part of the game. I killed Blackhorn 21 times on Normal and another 29 times in LFR hoping that shield would drop and it never did. It sucks, I know, but it makes you keep playing the game. Eventually I realized I had enough gear everywhere else that the small stat increases weren't going to affect my overall game play all that much. So I transmogged my 378 heroic dungeon sheild to the Grul's layer shield and forgot about it...