If you are worried about a gear gap maybe see if a highly geared healer/friend queues with you. The only thing your lower gear will do is make you harder to heal and not hold aggro as much as a high geared tank.
As was said above, tanks are pretty much instant random dungeons and so you should be able to gear pretty fast. Once you get your basic gear I would move to ICC 5 mans where there are some decent drops which will fill the gaps in your gear very quickly.
Good luck