I found the Python Brigadier utility on Github to download all BootCamp files for the current or a particular model of Mac. You can run it under OSX for download or Windows to download and install. It can force a particular model - like -m MacPro6,1 on a 5,1.
https://github.com/timsutton/brigadier
Very useful.
https://github.com/timsutton/brigadier
Very useful.