The Canon MP-E 65 can do macro shots up to 5:1. I've not been able to find anything like this for my Nikon system and you can't mount a Canon on a Nikon at all. Do Nikon or any third party make a lens that goes above 1:1 like the MP-E and will mount to a Nikon?
Good question, but the answer is NO, not just for Nikon but for any system that is not Canon.
As per the comments you got, there are ways to get that magnification but the lens is much more convenient. I have used one and it is quite awesome.