Below are links to posts that cover the tamable low-level rares that were added in patch 5.1. These posts include full maps showing where you can find them, screenshots, npcscan id's and other useful information. The number next to each zone represents the level range of the pets that you will find there. (This list is a work in progress.)
Elwynn Forest (level 5-9)
Tirisfal Glades (level 5-9)
Silverpine Forest (level 10 - 20)
Hillsbrad Foothills (20-25)
Wetlands (level 25 - 27)
Arathi Highlands (level 25-29)
Stonetalon Mountains (level 25-29)
Western Plaguelands (level 35-39)
Eastern Plaguelands (level 40-44)
Thousand Needles (level 40-45)
Badlands (level 45-49)
Felwood (level 45-49)
Searing Gorge (level 47-49)
Blackrock Mountain (49) *Need to be at least level 69 and BM spec to tame these rares
Burning Steppes (level 50-53)
Winterspring (level 50-54)
Swamp of Sorrows (level 52-54)
Silithus (level 55-59)