I'm playing a tavern in a dark forest map and I desperately want to make ice wine. But I can't figure out how to get frostberries - harvesting berries after frost doesn't seem to work, so I went to all winter maps to try and plant some, but that's not working either. Anyone know?

EDIT: I also don't have the option to build a rustic fermenting barrel. I can cheat to give one to a pawn and then drop it, but I can't build it anywhere, and when I do cheat, I don't have the option to make ice wine in it. Just mead, wine, ale, mulberry wine, and griffon berry wine.