There are three ways for u to get Tanking gear 1) buying or crafting 2) rep grind and 3) Instances. However, with all the dailys in wrath there is no excuse to be low on gold. For me I got most of my starter gear from wyrmrest accord. Argent Crusade and Knight of the Ebon blade rep vendors. which included chest, pants,feet, back. The rest was BS gear or dungeon drops. There is also some nice tanking items from quests.
So do your dailies, work on ur rep, do dungeons, and when possible do quests that give good tanking items. For me at lvl 80 i had my starter tanking gear in less than 2 weeks. Also don't forget about the new rune. Also if you need a good gear guide wowhead has a really nice post in the DK forums.