You can fish the Sea Pony in the waters surrounding the Darkmoon Fair. The drop rate on this pet is very good. Changes are, if you have been doing you monthly quests there you should have gotten is already.

lvl1 Water Jet
lvl2 Surge
lvl4 Whirlpool
lvl10 Tidal Wave
lvl15 Cleansing Rain
lvl20 Pump

I got this idea from one of my Twitter followers. Thank you!