Tempo books is no longer available as a separate product. Books features have been incorporated in Tempo Timesheets as of Timesheets 8.0. That's probably why you only see Timesheets in your list of installed add-ons.
For a little bit more background, see this link: https://tempoplugin.jira.com/wiki/display/TB/Tempo+Books+Installation+and+Upgrade+Guide.
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