No baking powder to be had? If you have cream of tartar on hand (or at least in your local grocery store), mix 1/2 baking soda (sodium bicarbonate) and 1/2 cream of tartar to equal the amount of baking powder you need. Baking soda is alkaline and cream of tartar is acidic, and so react with each other to create carbon dioxide gas (a leavener), which is the same reaction that the sodium bicarbonate and dry acid in baking powder create. Don’t mix ahead of time though, baking powder has added stabilizers that prevent premature reactions.
As a tip, I like to transfer baking soda into one of these tins and label it very clearly. These tins are much more robust, for, say, accidentally setting down in a puddle of water on the counter, and the wide-open top with the metal ledge makes measuring much easier.