The steps to do this manually are tedious, and there are many of them. Sometimes we just want to download and extract a copy of the installer for a given model.Apple can already download the correct installer for a booted machine model in OS X using the Boot Camp Assistant, so there's no reason we can't do the same within Windows. It's possible to use the Orca tool to edit the MSI's properties and disable the model check, but there are rarely cases where a single installer contains all drivers.
A Windows- and OS X-compatible Python script that fetches, from Apple's or your software update server, the Boot Camp ESD ("Electronic Software Distribution") for a specific model of Mac.