Zero (of the) sparrows were found dead. Yes but sparrows here is the object of a preposition, not the subject of the sentence.

"None" is singular because it stands in place of "not one." Therefore, "None of the passengers was found" is correct, although it sounds awkward and the use of "were" is more or less forgivable. But take out the prepositional phrase of the passengers and you still have the sentence "None was found."

(One episode of the "Beavis and Butthead" show had Butthead praising his favorite rock
band thusly: "These guys rock. There is none higher.")

But getting back to zero... Really zero is neither singular nor plural, mathematically speaking, since it is neither one nor many. To assign it any case is arbitrary, and plural seems to work as well as as singular. perhaps a more rigorous language would have a unique case for zero, but our languages evolved faster than our understanding of the concept of zero, so probably we were already set in our ways when it came on the scene.

For a very interesting essay on The History of Zero, see http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Zero.html

Now then, next question: what is tat and where do I get some?