Hello Paul,
Thank you for your email and your interest in our services.
Tickets for 2018 are not available yet for anyone, that is why they don't appear on the availability calendar. By the end of December is usually when the government opens purchases for the next year, even for January. The only thing is wait.
You can subscribe to receive the availability when purchases for 2018 are open: http://www.ticket-machupicchu.com/dispo/index.php?lg=en .
Best regards,