I think the horseshoe magnet generators are easily the best looking dynamo they made, In my humble opinion. I have previously wanted to try making a horseshoe magnet generator, but it's a fair bit of work haha! In this case, if parts are not on hand, I would think you could find a magnet that is pretty close to the right size and shape, available off the shelf. Whatever you decide to do, please let us know! I'm sure this isn't the only engine missing magnets on this forum haha!