Just look at this massive list of Timeless Isle pets. Not surprisingly, a lot of them come from the rare spawns on the Timeless Isle, as well as other sources.
To collect the Celestial pets, you will need to complete the Celestial Tournament ten times.
Moon Moon drops from the new Darkmoon Faire boss – Moonfang
Unique Abilities: Moon Fang, Moon Tears, Moon Dance.
There are three engineering pets: two are made while one is obtained from Blingtron.
Pierre is a mechanical pet that doubles as a cooking fire
Blingtron Gift Package
Ashleaf Spriteling – Drop from Leafmender
Azure Crane Chick – Loot from a Crane Nest
Dandelion Frolicker – Neverending Spritewood
Interact with the Neverending Spritewood (purple rare spawn crystal) and kill Scary Sprites (note these are the larger sprites which can randomly spawn as opposed to the smaller Angry Sprites) – (45.4, 73.3)
Drop from Imperial Python
Drop from Gu’chi the Swarmbringer
Gulp Froglet – Drop from Bufo
Jademist Dancer – Drops from Jademist Dancers
Jadefire Spirit – Drop from the Spirit of Jadefire
Ominous Flame – Drop from Foreboding Flames
Skunky Alemental – Drop from Zhu-Gon the Sour
Spineclaw Crab – Dro from Monstrous Spineclaw
Ruby Droplet – Drop from Garnia
To reach Garnia, you need to use the Timeless Isle Airways
Purchased from Ku-Mo for 7500 Timeless coins
Harmonious Porcupette – Mistweaver Ku – Requires Shaohao (Pathwalker) rep – 7500 Timeless coins
Vengeful Porcupette – Bought from Speaker Gulan – 100 Bloody Coins
Siege of Orgrimmar
Droplet of Y’Shaarj – Sha of Pride (Flexible, Normal or Heroic)
Kovok – Paragons of the Klaxxi
Gooey Sha-ling – Sha of Pride (LFR or Flexible)
Blackfuse Bombling – Siegecrafter Blackfuse