Ah, the Hand of Vengeance, supposedly this is Lady Sylvanas contribution to the war effort in Northrend. On paper they are an equal part of the Horde Expedition working together towards the ultimate defeat of their former master, Arthas, or The Lich King. However all is not as it seems amongst the Hand of Vengeance. The military members are in no way focused on assisting the rest of the Horde forces, rather their single task is to assist the Royal Apothecary Society members scattered about their various bases of operations in producing and distributing The New Plague. The presence of the Deathstalkers further demonstrates this.
As a result of the Hand of Vengeance's single focus they are not very prevalent in Northrend. Specific quests for this faction can only be located in two places Howling Fjord and Dragonblight, (A total of only 53 in all.) Howling Fjord has the largest portion with its four quest hubs, Vengeance Landing, New Agamand, Ghostblade and The Apothecary Camp. In Dragonblight their focus is solely in Venomspite even though the final result will be seen at Kor'korn Vanguard, or more correctly at the Wrathgate just below it.
The discerning player will soon pick up on the undercurrents as quest after quest you assist in "perfecting" the New Plague and Royal Apothecary members work at adapting it to the Northrend environment. Failure is NOT an option for this faction as their policy of no mercy for the captured clearly demonstrates.
Before patch 3.3 getting to exalted with this faction was an impossibility. There were NO repeatable quests available and few quests outside of the two aforementioned zones that offered spill over reputation for them. With patch 3.3 however Horde players can now earn reputation with the Hand of Vengeance both by running level 80 dungeons while not wearing a reputation granting tabard or by doing the daily quests offered at the Argent Tournament in Icecrown at Champion level. This simple change has made all the difference.