$ curl -O https://bootstrap.pypa.io/get-pip.py
$ ./pypy-2.1/bin/pypy get-pip.py
$ ./pypy-2.1/bin/pip install pygments  # for example

alias pypy_pip='./pypy-2.1/bin/pip'

pypy -m pip install [package]

$ whereis pip
pip: /usr/local/bin/pip /usr/bin/pip