If you are streaming you can actually request review copies of a game to play it on stream. How many followers and subscribers you have does not really matter as much as people think, and streamers with as low as 100 followers gets keys most of the time. However, more followers means a bigger audience, and increases your chances to get a key.
Some game devs give away keys to all the people that ask, while others has a set limit, so if you don't get a key on your first try, don't be afraid to contact other developers.
Before you begin you need to have a streaming related e-mail address that is verifiable on your Twitch account and on social media. This will let the game devs know that you are not a key scammer without too much trouble. Also try to make sure your social media and stream is somewhat professional looking before sending e-mails and ask for keys.
Once you are ready, find the correct e-mail to the developer or publisher you want a key from. Look for an e-mail that is related to "Press", "PR" or "Media" or something related to that, and if you cannot find one, use the contact form on their website, or just use the general contact e-mail.
Now it's time to send the e-mail. Make sure to include the following:
- A friendly greeting.
- You real name and your Twitch name.
- Links to your stream, Youtube and social media.
- What game you want, and what system you want it for.
- A few sentences about why you want to stream the game. Tell them about similar games you have streamed etc. Don't make it too long!
- A thank for your looking at your e-mail.
Now send it, and make sure it's not too long, because most devs would rater spend their time doing other things than reading e-mails.
After this, it's waiting time. Just cross your fingers, and don't be afraid to try again once your stream grows if you get a negative reply.