for all those who are doing this for the item reward,then know the following:
this quest is available only after having done many thousand needles quests before. The guy that'll start the event for this quest is [npc=40027], the co-owner of the Fizzle and Pozzik's Speedbarge, on the lower right corner of the thousand needle's world map.
I started ALL the quests by going at New Thalanaar, which is in feralas, on the middle right of it's world map. The quest giver was fighting grimtotems behind the tower. From there,i had to do all the quests given to me until Fizzle finally decided to give me the quest called " Free Freewind Post ".
The questgiver of Darkcloud Grimtotem has its location unknown because it's actually someone following you once you do a few of the quests the NPC called [npc=41392] gives you. Once you start the quest given by [npc=41444] called "Save the Sentinel" a few quests later if not right away, the sentinel will follow you. Just do her quests and you'll fall on this quest at one point.
PEOPLE WITH PETS ( HUNTERS AND LOCKS ) : dismiss your pet as soon as you get the sentinel quest. If you don't ,you'll realize you won't have any more quests and be stranded questless on that island. If already so, just dismiss your pet and run between the needle pillars associated with the grimtotem,and the sentinel should appear.