I can't install pip for python 3.5

My friend owns a Raspberry Pi, and no matter what we try to do we cannot get pip3 installed for python 3.5. We’ve tried get-pip.py, but that only works for 2.7. We’ve tried sudo pip install -U pip, but that only upgrades pip2.7. We’ve tried sudo apt-get install python3.5-pip, but the package doesn’t exist. We’ve tried sudo easy_install3 pip too. I can’t figure out how in the world to do this.

(pip3 works, but that’s for /usr/bin/python3, not /usr/local/bin/python3.5.)

Help?