There is a site called Keymailer where game developers can issue you keys for the game you request. Keep in mind there is like a 10% chance you will get a key. I think the more followers you have on your YouTube/Twitch/Twitter the better chance you have.
Keymailer's requirements are
-50 subs/followers on YouTube/Twitch
-tag your posts using the official tags located on the game's page. After you pass the requirements your page will be accredited. The process depends on how many followers your channel have.
In a way, devs offer you a free key in exchange for reviewing or playing/streaming the game on your channel. NO hefty requirements for this site. Only 2 simple rules.
Site: Keymailer.com
