I don't think so. If there is, I think it might be that the Hero needs to be in one of the nations bordering an enemy, so it might be worth trying that just in case. A messenger will appear telling you one's there.
Since there's no penalty at all for taking too long with the main story, you can just spam the months until one appears. The stones cost 5000 each, so you might want to delegate some nations to Develop if you don't have the cash. Or you can just set them all to Train so your links go up.
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