It looks like Blizzard changed this quest around with 4.3. Lethyn Moonfire apparently no longer gives out this quest. Here are links to WoWHead to help you find the quest giver depending on your faction. This affects both the Titles guides (Guardian of Cenarius) and the Reputation guides (Cenarion Expedition).
http://www.wowhead.com/quest=9961 - Alliance
http://www.wowhead.com/quest=9960 - Horde
http://www.wowhead.com/quest=9961 - Alliance
http://www.wowhead.com/quest=9960 - Horde
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