The difficult part would be finding the braided ball that connects the ponytail. If you can find that, then any long blonde Cher wig would do, and you can cut it accordingly. I actually think M had different lengths for the ponytail. It seems longer in Japan then a little shorter in the US shows.
If you want the big effect, search for a good lace-front, then you can spirit gum the forehead and it won't flip off. And get blonde hair clips for the back, which M used (if you're going for exact look) ;)
If you find something and are successful, PLEASE post pics would be great to see! Good luck!