In my (recent) experience of this kind of material (based on my old experience reviewing all kinds of security literature, see here and here), the "giveaway" promos from vendors tend to be "cut down" versions (first three chapters?) of existing books. Are you looking to get copies to read yourself (see the vendors), or are you looking for material yourself, to use as giveaways (see publishers)?
Other posts: https://community.isc2.org/t5/forums/recentpostspage/user-id/1324864413
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