As Ross points out you need to use Advanced GAM. After that IIRC it's a two step process. First you'll need the ID of the folder of interest, then you can pull the file list. So, I think something like this:
> gam user <someUser> show fileinfo teamdrive "<team drive name>" teamdrivefilename "< folder name >" fields id,title
That will get you the ID of the folder, then you can ask for a list of files in the folder.
> gam user <someUser> print filelist select <folderID from previous step> fields owner,id.title
That should get you a list of all the files in the folder. It's a non-obvious process and Ross may have a much slicker way to do it.