Solution 1 :

For some reason, installed in /usr/bin/, instead of under /usr/local/bin.

The following in my .bash_profile works...

source "/usr/bin/"
export WORKON_HOME="/opt/virtual_env/"

My install seems to work fine without sourcing virtualenvwrapper_bashrc

Solution 2 :

Alternatively as mentioned below, you could leverage the chance that is already in your shell's PATH and just issue a sourcewhich