Well, you only have to kill 1 of them so start from 1 and keep looking if they have spawned yet or not. It may make it easier to make a macro with /target RARE CREATURE NAME. Here's a list of the mobs and their locations.

Borean Tundra

1. Icehorn South of Deaths Stand 85,47
2. Fumblub Gearwind East of Fizzcrank Airstrip or Southeast of The Geyser Fields
3. Old Crystalbark Coldarra (Circular pattern around The Nexus, he's a tree )

Dragonblight

1. Crazed Indu'le Survivor Roams around Star's Rest
2. Scarlet Highlord Daion Pretty big patrolling radius: 85,37 - 72,70
3. Tukemuth found East and Northeast of Wyrmrest Temple

Grizzly Hills

1. Grocklar South of Conquest Hold or around Granite Springs
2. Seething Hate 28,45 or 34,49
3. Syreian the Bonecarver Start at 67,39 she patrols north

Howling Fjord

1. King Ping Roams around the border of the island of Kamagua
2. Perobas the Bloodthirster Roams around 53,12 and 50,4
3. Vigdis the War Maiden East,Northeast of Nifflevar

Icecrown

1. High Thane Jorfus found around 70,40 and 47,86
2. Hildana Deathstealer 58,63
3. Putridus the Ancient Spawns at 67,56 and patrols south

Sholazar Basin

1. Aotona - North of Rainspeaker Canopy roams between (44,70 and 55,51 )
2. King Krush (27,61 28,71 63,84 36,30 )
3. Loque'nahak Spawns at 28,43 but on a long timer

The Storm Peaks

1. Dirkee Spawns at 37,59
2. Vyragosa 34,44

Zul'drak

1. Griegen Southeast of Ebon Watch 24,77
2. Terror Spinner 53,31 72,25 75,65
3. Zul'drak Sentinel Patrolling route;look from 48,64 all the way to Griegen