User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-3062343-20120121010046

Apparently, Hungry Deviljho doesn't have any quests specifically to hunt it. It seems that there is a certain percentage chance that it will appear in the "Advanced" (the ones that appear and disappear randomly) quests, as well as a few others. Whether or not it is selected to appear resets after a day passes in-game. Apparently Qurupeco and Sub can still summon it when it is not selected to appear though. So, it randomly appears in quests which randomly appear. It also only has one unique item, which is required to make the Vangis X armour and the final upgrades to Deviljho weapons. Someone on GameFAQs explained it more in-depth, as seen here.