http://kamikaze.thing-printer.com/apt/

Add this repository to /etc/apt/sources.list as:
deb http://kamikaze.thing-printer.com/apt ./ # Kamikaze repo
For packages from Stretch, add this:
deb [arch=armhf] http://kamikaze.thing-printer.com/apt/ stretch main
Import verification key with:
wget -q http://kamikaze.thing-printer.com/apt/public.gpg -O- | sudo apt-key add -