Cargo FP Uploads
Most of this lot are still 'parked up' awaiting flightplans.
JF have been promising to add more cargo flights to TG since forever and, as you say, there are many repaints in TG without any flightplans (not just cargo planes, either).
As an FSX user, I downloaded representative flightplans for each TG cargo carrier from AIG and used AIFP3 to substitute aircraft with TG repaints.
An even easier way would be to download AIG's AI Manager and just add some of the missing cargo carriers (if you have P3Dv4, it's an absolute breeze using the One Click Installer).
The AIG stuff will run alongside TG without any problem..and add a bit of variety too!
Hope that helps, Max!
Cargo @ VHHH using AIG OCI only
In a nutshell you have to add them yourself, one way you can do this is at your addon airports you will have flightplans not compiling due not enough gates, you can open TG click the departure tab at the top scroll down to the CODE for your airport then edit a plan, example change the aircraft from EasyJet 737 to ABY FDX FedEx A300-600 or any cargo you like, recompile then check, I have added over 1500 Cargo aircraft using this method.