If I can't find anything named "scallions" at the store, what else can I look for?
According to Wikipedia:
In the grocery stores I've been to most (east cost of US), if they aren't called scallions, they're called green onions. I've never seen grocery stores label them with any of those other names from Wikipedia (though I've seen recipes calling for syboes).
Then of course there are stores / vegetable stands where nothing is labelled, in which case knowing what they look like is the most helpful ;) (Google image search yields plenty of decent results.)