patch 2.4's new non-combat Phoenix Hatchling pet can be found: it drops from Kael'thas, in Magister's Terrace. This is kind of cute if you think about it, since the version of Kael'thas in the Eye drops the Ashes of Al'ar. Big Kael'thas, big phoenix; little Kael'thas, little phoenix. According to MMO-Champion, it drops it normal mode, but not in Heroic. If you need any help with your normal-mode Kael'thas strategy, check out this video. Still unknown is what the drop rate is. I'd guess pretty low, as these "frill" items tend to be that way (Baron's mount, anyone?).