Bash not recognizing packages installed using pip-3.6
MacPorts may not have put things where you think, see here. Did the pip-3.6 command work? What do you get when you which pip-3.6? 

Have you considered Homebrew over MacPorts? pip3 comes automagically with python3.x with Homebrew. It also has a virtualenv package that is easy enough to uninstall if needed.