Beautiful! Unfortunately, some link rot seems to have occurred, the packages can now be found on old-releases.ubuntu.com. Updated snippet for 20.10 in 2021:
wget http://old-releases.ubuntu.com/ubuntu/pool/universe/p/pygtk/python-gtk2_2.24.0-6_amd64.deb
wget http://old-releases.ubuntu.com/ubuntu/pool/universe/g/gimp/gimp-python_2.10.8-2_amd64.deb
wget http://ubuntu.cs.utah.edu/ubuntu/pool/universe/p/pycairo/pyt
hon-cairo_1.16.2-2ubuntu2_amd64.deb
wget http://mirrors.cat.pdx.edu/ubuntu/pool/main/libf/libffi/libf
fi7_3.3-4_amd64.deb
wget http://lug.mtu.edu/ubuntu/pool/universe/p/pygobject-2/python
-gobject-2_2.28.6-14ubuntu1_amd64.deb
sudo apt install gimp gimp-plugin-registry gimp-gmic
sudo dpkg -i libffi7_3.3-4_amd64.deb
sudo dpkg -i python-gobject-2_2.28.6-14ubuntu1_amd64.deb
sudo dpkg -i python-cairo_1.16.2-2ubuntu2_amd64.deb
sudo dpkg -i python-gtk2_2.24.0-6_amd64.deb
sudo dpkg -i gimp-python_2.10.8-2_amd64.deb