If Tarby is not there, you'll need to wait for him to spawn (clocked at 15 minutes).
Hail Tarby and click a few responses to begin a short ring event where three waves of wolves spawn and try to kill him. Note: ALL group members must hail Tarby.
You must defeat three waves of progressively more difficult wolves. -First wave is level 28
The final wave of wolves also has one larger, more difficult mob.
When the wolves spawn, taunt or hit the wolves first. If they attack Tarby, he will fight them and LOCK the encounter.
PAY ATTENTION! Even if you managed to "get" the encounter without Tarby locking it, Tarby will still fight! Make sure NONE of the wolves is targeting (and thus fighting) Tarby. He has very few hit points and will die quickly. If he goes down at any point, you sit for 15 minutes waiting to start this all over. A good strategy is to pull the mob AWAY from Tarby so nothing gets close enough for him to attack.
Once the wolves are defeated, hail Tarby (have all members time your hails so you don't have to wait for Tarby to respawn) and pick him up.