That's because there aren't many books coming out of the Seitokai world which is the primary group doing Batto Ho. The soke has books out, but it's not easy to gain access to them. They are only available in Japanese and the set is around $500.
Nanno's book is about the closest you're going to come to what you are after.
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Iaido -
Breaking down bad habits,
and building new ones.