You can only get them by an old trick that most of us who've been playing for years know, but almost everyone in the roleplaying guilds know because it's a popular way to be punished in character, making someone build a wall of water barrels. You go to cities with docks and fishers guilds, (Britain and Trinsic have the most), and you take a pitcher of water, and an empty pitcher. If a barrel has water in it, use the empty pitcher on it, put the water back in the pitcher, then take it out. You can now pick up the barrel. If the barrel is empty, pour the one pitcher of water in, then empty it again. You can now pick up the barrel.
Enjoy!