Wait, just remind me how did the topic cannibal orcs go to the theologic future of the orcs and the elves and all those people. but I do think that after mordor fell, there is still a lot of orcs creeping around the mountains if that is what you are talking about.

Just a couple of points in reply to some questions raised in this thread: AFAIK, the only time Tolkien refers specifically to the idea of orcs eating each other is in TT, 'The Uruk-hai'. There are three groups of orcs present: those from Isengard under Ugluk; those from barad-dur under Grishnak, and a bunch of smaller orcs from Moria. Ugluk tells the revolting members of the  other two warbands that he serves Saruman, who gives them man-flesh to eat. To which  Grishnak nastily replies 'It's orc-flesh they eat, I'll warrant', thus leading to a punch-up, in which several orcs lose their heads. But note: none of them get eaten. The movies are not a safe source for lore..

Later in the TT, Sam finds traces of 'a dreadful feast and slaughter' amid the loveliness of Ithilien ('Of Herbs and Stewed Rabbit).  Burned and broken bones and skulls in a ring of scorched earth; but not an ancient site. Tolkien tells us there were other signs of despoilation by orcs and other servants of the Dark Lord. My guess is that orcs killed and ate Men in that place; most probably men of Gondor.

As to how Sauron fed the armies of Mordor: later still, we're told of the great slave-worked fields in the south of the country, around 'the sad inland Sea of Nurnen', and the roads going off south and east to tributary lands, which brought in food and booty and fresh slaves. 

Tolkien would have had some training in logistics as an officer in an infantry battalion during the Great War. He'd have known about this sort of thing, and indeed (as attentive readers have noted) all of his characters' movements are affected by several factors; food supplies being one.