You can download it here, and run it at a DOS prompt:
Each kindle needs its own set of libusb-win32 device drivers installed, to work with fastboot for windows. There are multiple ways to do this, and multiple versions of libusb drivers for windows.
You can read some details about how *I* installed them for my K4 and Touch here:
You still need to know which libusb-win32 version, and what installers to use, and more (that you can learn from the libusb websites). More information will be provided later (perhaps in a wiki page). Hopefully there is enough information at the above links for you to figure out how to use it now if you need it.
This eliminates the problem of needed Windows for MfgTool and linux for fastboot, and the problem of the kindle dropping out of fastboot mode when the USB connections is disconnected or reset (by rebooting the host PC or VM). But it has the added complication of needed Windows device drivers.
At least there are alternative methods of using MfgTool and fastboot now, so you can use whichever method works best for you.