Baking powder can be substituted for baking soda; it takes about three times as much baking powder as baking soda to get the same rising effect.
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Buttermilk isn’t a common item at college supermarkets….obviously. So I made my own: 1 tbsp lemon juice or white vinegar into one cup milk and let stand for ten minutes. It isn’t as thick, but gets the job done.
That’s all; sweet and to the point, just like the Soda Bread.
(Info from Cooks Illustrated. If you don't have a subscription, I highly recommend it. Science, Cooking, Eating. What better?)