It takes about 2 months if the drop rate of shadowfrost shards wasn't low as hell.
"The fragments are dropped by bosses, or their chests, in Icecrown Citadel on 25-player normal and heroic difficulty only. The drop rate is approximately 25-50% for normal mode bosses and 51-99% for Heroic mode bosses" -
http://wowwiki.wikia.com/wiki/Shadowfrost_Shard
I'm a rogue, I really don't care about Shadowmourne, but it's kind of unfair after all these years you finally enable it and still has to be harder than it actually is.