Setup

Make sure python is installed
Run pip install requests if you don't already have it installed
Put your names list file next to checker.py. Make sure its called names.txt
Now open checker.py.
It will then check all the names in your list and write all available names to available.txt

Info

This isn't the most efficent checker but due to Twitch's extremely lenient rate limit you can check around 10k names every minute