This DLC item is currently part of the Trainz Preview Pass and only available to people with a Gold Membership.
What is Trainz Preview Pass?
Members with Gold Access will have immediate access to a range of DLC items direct from the Trainz Content Creation Program, to install and experience before their official release.
For those without a Gold Membership this DLC should become available for general purchase within the next month. If you wish to gain access to future DLC items released as part of Trainz Preview Pass, you can sign up to a Gold Membership HERE.