Добавьте эту строку в вашу сборку.
index = https://pypi.python.org/simple
Индекс
An alternate index location.
This can be a local directory name or an URL. It can be a flat collection of distributions, but should be a “simple” index, with subdirectories for distribution project names containing distributions for those projects.
If this isn’t set, then https://pypi.python.org/simple/ is used.
Из документации сборки.