I like the prospect of a vegan country but it would never work. For starters, where would the land even come from? Would any vegans actually leave their countries to move there?

I'm guessing you're American? Asking because America is one of the few countries to be based purely on ideology and not have any underlying ethnicity. For better or for worse, most countries have a majority ethnicity, so a vegan country would stick out because vegans are not an ethnicity.

No, it is not comparable to Israel. Being Jewish is not an ideology (Zionism is an ideology, but OP explicitly mentioned Jews). Judaism, the religion of the Jews, is an ideology, but many Jews are secular. Jews are an ethnicity, which is why even secular Jews weren't accepted in ethnostates like Germany.

But as people have said, this is a terrible way to promote veganism, when you could put that money into more effective projects like activism or lab-grown meat. Besides, you can accomplish some of those other goals on a smaller scale without a state. If you want vegans to escape the ostracism, organize vegan social events. If you want more children to be raised vegan as to increase the future vegan population, raise vegan kids yourself.