itch.io

I only know of two bigger studios making it work. Kagura Games and Otaku Plan.
But if you somehow manage to get your hands on a steam key you can activate it on your account.
Problem is most indie devs i contacted couldn`t sell me a steam key.
PS: I personally just like to have all games on steam since I already own 300+ paid games. So i kind of collect my games there.

Can I get my hands on a steam key?
Germany blocks nearly all 18+ h-games, so I can only purchase keys to activate the games on my account.