Does an iOS virtual machine for Windows exist? If it doesn't are there any reason why it couldn't?
Simple answer: No.
Apple does not allow iOS to run anywhere else but iOS devices (iPhone, iPad, iPod touch) and the Xcode simulator. You could simulate OS X on your Windows VM application and then use Xcode to simulate an iOS device, but this would be really taxing on your computer and really not worth the effort, but you cannot simulate iOS directly on Windows because of chipsets and Apple preventing it.