AppleScript Application - Path of folder in 'Supporting Files'
The "Folders" in the Xcode sidebar are "groups" and not filesystem entities. In your project there is no "Supporting Files" folder on disk. 

That said, you might try putting a dummy file in your target folder on disk, adding it to the project, and using the snippet you found to get a posix path to the dummy file. Which you can shorten to get the path to the target folder. You would want to remove the dummy file after you copied the folder of course.