The Terrible Turnip might be listed as a zone drop, but the hunt for it might not be as vague or broad as implied.
According to some comments on the beta forums and from WoWhead, this pet might be from your very own Tillers farm.
I can't confirm it yet, but it sounds as though certain plants have a chance to drop an Ominous Seed when harvested. Or maybe the vegetable depends on which plant Jogu recommends to plant? Anyway, the seed then produces (or has a chance to produce) the Terrible Turnip.
Either way, this PLUS the Red Cricket from Sho just gives us even more incentive to tend to our farms!
Sheesh, there's going to be so much to do in MoP. From Pet Battling, leveling, capturing, and collecting to reputation and profession grinding and farming - I wonder if I'm going to still have time left in the day to raid with my guild lol. :P
Edit: I just planted some Striped Melons, Scallions, and Jogu recommended some Pink Turnip for me, so we'll see what comes of it all!