Such a situation exists for peoples who have no contact with the industrialised world and live in a geographical area where the local vegetation does not allow them to follow a vegetarian diet.
I believe the reason it is not wrong for animals such as lions to eat meat is that two conditions are met at the same time: lions naturally need meat to survive, and the ecological balance of their habitat depends on lions hunting.
If both conditions also apply to people, as they do for some non-industrialised peoples, then I believe those people are ethically justified in hunting, just as lions are. So I believe eating meat is ethically permissible in some situations.
I also believe cannibalism is ethically permissible in some hypothetical situations. For example, suppose a group of people were shipwrecked on a deserted island and would die before being rescued unless they ate one another. In this hypothetical scenario, I believe cannibalism would be ethically permissible.
However, the fact that eating meat is ethically permissible in a few hypothetical scenarios should not be an excuse for us when the conditions in those scenarios clearly do not apply to us.
Although this should be obvious, I feel obliged to emphasise that my answer to this question, like my answers to many others, is my personal opinion and does not necessarily represent the views of other animal-rights advocates.
More answers: Vegan Ethics FAQ.