How many clears? According to wowhead, the mobs in the Pit of Saron have a 1% chance or so to drop it.
Update:
I've just decided to grind for the hilt again on my warrior (For my pally, I had intended to get the mace which I had designed an entire transmog around - which I discovered to my dismay to be impossible - but quite fortunately, the sword works well with my preexisting warrior transmog!), and it dropped on my second run of Pit of Saron, not 6 minutes into my farm (my runs are all the trash packs on the southern side of the pit that I can rally up in a couple of minutes or less), so it looks like the droprate is indeed 1% for all the mobs. It may be just good RNG, but the commenters on WoWhead, the official forums, and here on this very thread would seem to confirm WoWhead's average of 1% droprate per mob.
TL;DR, if you want the hilt, go run the dungeon for a bit and it WILL drop sooner or later. 1% droprate really adds up when your slaying dozens and dozens of trash per run every few minutes, and you can easily fit them in between raid/BG queues.