One option has been mentioned. Gear the tank up with some randoms. Even if people give you crap, tanks get insta queues so it wont take long even if you get vote kicked a few times. I remember gearing up my tank this way when the dungeon finder first came out and it only took a good solid weekend to be decked fully decked out in the best Triumphs could buy. It made a HUGE difference having double the hp when I was done.

Next is gear. Tell me you have a blacksmith. there are a lot of i200+ epics you can pick up.

Arena gear. Make a 5x arena team and just afk out of your 10 games each week. There are some very nice ret items to be had. Use your stonekeeper shards to buy honor. You're not raiding so who cares if the item has resiliance on it instead of expertise.

Reputation gear. Each faction in Northrend has some decent blue and epic gear to be had. Make sure you have on the right tabbard when you're in heroics and do some quests/rep grinding.

Regular ICC 5mans. They are not heroic but if you can get even one boss on farm its an emblem and i219 loot

The rest will come with time. The bosses that are killing you now like CoS will go down like crying babies with better gear. Gundrak snake boss wont even be alive long enough to cast poison nova and meathook will have a 45k hp tank to kill instead of 26k. Also use everything to your advantage. Drums of the Wild. Runescroll of Fortitude. Get some HP/ATK boosing food. Hell, if your rich even flask up. It can mean the difference between struggling and wiping, to making things your bitch while your gearing up.