How do I access my iBooks on iCloud? There is no icon for iBooks or options to include iBooks on my iCloud whatsoever.
Apple did not write a web application to access books via a web browser, so you can't access your iBooks via iCloud.com. Access to that data is only possible on a Mac or an iDevice with the iBooks application.

It might be an interesting feature though. You can submit feature requests to Apple using the feedback form on apple.com.