I'm not sure where they're originally from, but they grow really easily so we grow them on most spaceships. They're berries, big and blue-purple and square-ish. You don't have them here, I've checked.
Oh. If it's for the caffeine, dissolving caffeine pills in Coke works too. But I'll try Mountain Dew! I'll add it to the list of new things to get when I'm shopping.