I did this as soon as I got the quest.. or somewhat after. ya... do a 'event' first. (Like the 'I am (not) basch' one.)

The smallest area of the Eastersands has it. It's a little area that leads nowhere but is considered one of the most southernly regions by the game. Should show you where it is. Go get the vane at your leasure, the beast is smurfing tough. (Or just span out your mist abilties.)