Hi @fmaillet, yes for now the Interaction Library is only available on our Landing pages for which the link has been posted above. Sorry for any inconvenience.
With regard to Head Tracking Data on the Pro SDK, I was unable to find that variable exposed (http://developer.tobiipro.com/net/dotnet-sdk-reference-guide.html) so I suspect not. However, it would be best to double-check with the Tobii Pro Support team about this @ http://www.tobiipro.com/contact/contact-support/
Please let us know if we can provide any further assistance. Best Wishes.