You'll have to buy every single piece of gear that is possible to purchase w/ Conquest Emblems first. That takes about 520 Conquest Emblems, although you already have a few pieces, so it will take less for you.
You can get roughly 50 Conquest Emblems per day if you run all 12 H dungeons per day, which means roughly two weeks worth best case scenario. Just farm the hell out of 5mans.
Go to the Horde Conquest Quartermaster in Dalaran, look at everything they have, and if it is an ilvl upgrade to your current gear (or takes it from blue to purple), add that to your shopping list. There are some slots the Conquest Quartermaster does not have, like a cloak iirc, that you'll need to buy from the Valor Quartermaster instead.
Add up the emblems cost for all of that, figure out a plan for farming all those emblems, and go do it.
Also do the H daily everyday to start collecting triumph emblems. It takes 15 days to get the Triumph T9 shoulders and 15 more to get the T9 hands, then another 25 days for the chest and 25 for the helm. Close to the 3months, unless you can get into a ToC10 group at some point during that grind.
Use
WoW Heroes - World of Warcraft PvE character info & ratings to measure your progress, it will give you an idea of when and how ready you are to tank certain raid content.
Yes that's a lot of farming, and you'll be complete burnt out w/ 5mans by the time you're done, but getting as close as possible to BiS gear in every slot is the minimum expected of anyone who wants to tank ToC 10. Most guilds with any prospect of success will take nothing less, and even then the odds are against you, and you may find you'll have to go dps initially in order to get into one.
On the bright side, as a tank you'll have no problem putting together pugs for it all and chain farming them, and will probably even meet some skilled, chill players along the way, some of whose guilds might need a decent DK tank.
G'luck!
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