Good point Adam, unfortunately quarter sawn is best ...but probably tricky to get....especially where you are. Try Cromarty Timber. They are a bit father south from you but superb at cutting out just the right wood...if they have it.
When you do come to put this together, on one of the sides of the staves (preferably the same one all the way round) take a thickish piece of wire and gently tap it with a hammer until you have a shallow dimple running along the length of the side of the stave. Then take a couple of wispy shavings with a good sharp plane. Once all assembled as the wood takes up moisture and the parts expand to seal up the barrel the dimple rises and becomes a small bead that acts as a waterproof seal.