The likely reason you are not seeing your network drives is detailed in a discussion here:

In short - this is likely happening on your computer because TPTransfer is running in Administrator mode (which allows you to transfer TP4 files that are open in TPDesign4), and likely your network drive was mapped using a Standard user account.
So, if you create mapped network drives using Administrator rights, for example, through Command Prompt (Admin) and type "net use z: \\server\path", the network drive will be available in TPTransfer when running in Administrator mode.

More details on the "net use" syntax can be found here: