Emerald Drake

Reward from: Awake the Drakes.
List of the different zones and instances where you're able to obtain the mounts:

[zone=4500] (Borean Tundra)
Both mounts drop (not necessarily simultaneously, but possible) from [object=193905] after you kill the one and only boss [npc=28859]. Drops from either difficulty.

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• [item=43952]
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• [item=43953]
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[zone=4493] (Dragonblight)
The mounts have a 100% chance to drop if you leave all three Twilight Drakes ([npc=30451], [npc=30452] and [npc=30449]) alive and then defeat the boss [npc=28860].

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• [item=43986] (drops from 10-man difficulty)
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• [item=43954] (drops from 25-man difficulty)
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[zone=4100] (Tanaris)
To loot this mount, you must clear the instance on Heroic difficulty and reach the NPC [npc=32273] within 25 minutes (timer available). Drops with a 100% certainty.

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• [item=43951]
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[zone=5892] (Tanaris)
This mount drops on all difficulties. Loot the [object=210079] after defeating [npc=56173].

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• [item=77067]
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[zone=2159] (Dustwallow Marsh)
Drops from [npc=10184] on all difficulties.

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• [item=49636]
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Dragonblight
Sold by [npc=32533] on top of the Wyrmrest Temple. Requires you to be exalted with [faction=1091].

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• [item=43955]
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Shadowmoon Valley
You need to complete the quest Lord Illidan Stormrage and be exalted with [faction=1015] in order to buy this mount from [npc=23464] (offers the quest Malfas the Purple Netherwing Drake). If you already completed the quest, the drakes can also be bought from [npc=23489] for 200 gold each.

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• [item=32860]
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Get it by doing this achievement: Awake the Drakes

Scratched my head when this was my rarest mount.