In order to get the missing CN SD751 bogey, you must register your game here:
https://www.auran.com/planetauran/SN_Enter_Serialnumber.php
This will open more of the forums and a special area to the versions that you own.
If you had registered your game, and it isn't showing up, contact the helpdesk so they can fix it. Link on top.
Failure to register your game can lead to the community to continous remind you to register your game, and if the mods / admin starts seeing you are being reminded, might ban you - I had seen this happen.
It will also lead to us assuming you are using a pirated (aka illegal) copy of Trainz, and therefore will entitle you to 0 help
So please do us a flavour, and before asking on where you can get the bogey's, register your game
Cheers