Try this, this is the most simplest solution.
sudo gedit /etc/apt/sources.list
Add these lines in the end of the file:
deb
http://http.kali.org/kali kali-rolling main contrib non-free
deb
http://security.kali.org/kali-security kali-rolling/updates main contrib non-free
deb
http://http.kali.org/kali kali-rolling main contrib non-free
deb
http://security.kali.org/kali-security kali-rolling/updates main contrib non-free
deb
http://http.kali.org/kali sana main non-free contrib
deb
http://security.kali.org/kali-security sana/updates main contrib non-free
Then add the key:
sudo apt-key adv --keyserver pgp.mit.edu --recv-keys ED444FF07D8D0BF6
Then run
sudo apt-get update
Now you should have most of the packages that is present in Kali linux, mitmf is one of them.
sudo apt-get install mitmf