Of course you can use Debian mirrors.
Simply add this line to your /etc/apt/sources.list:
deb http://deb.debian.org/debian stable main

Reading package lists... Done
Building dependency tree      
Reading state information... Done
ranger is already the newest version (1.7.1-1).
0 upgraded, 0 newly installed, 0 to remove and 324 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Setting up python3-uno (1:5.2.7-1) ...
Traceback (most recent call last):
  File "/usr/bin/py3compile", line 25, in
    import logging
  File "/usr/lib/python3.5/logging/__init__.py", line 26, in
    import sys, os, time, io, traceback, warnings, weakref, collections
  File "/usr/lib/python3.5/os.py", line 113, in
    from os.path import (curdir, pardir, sep, pathsep, defpath, extsep, altsep,
ImportError: cannot import name 'curdir'
dpkg: error processing package python3-uno (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
python3-uno
E: Sub-process /usr/bin/dpkg returned an error code (1)

It can't access the current directory variable.
Probably you are in an directory which Python can't access.
Try "cd /root" before installing it.
You run apt-get as root so it should have access to this directory but probably not to your home directory.