No problem Chris. You can get the S&C pack, yes.
First of all though, you need to register your copy of Trainz Mac 2. I seem to remember it being like Trainz Mac - Click on 'Settings' from the launch window and do it there.
Once your registration has gone through, on the launch window click the 'Purchase Content...' button; it will be listed there.
Let us know if you need any more help.
Regards,
Alex