Honestly, streaming to just get stuff for free is a pretty poor way to look at it. Itís fantastic when companies and devs place trust in you to promote their products and content, it can be fantastically rewarding, but not as an end goal.
However, networking with various companies can be a fantastic way to raise your profile, especially when you showcase anything they send your way. You will gain value in their eyes the more of this type of work you do off your own back, without being sent the items for free.
However, ultimately, the best thing to do is to simply ask. Drop an email, a tweet, whatever, introduce yourself and speak about your passion for what they do. Start smaller and gradually grow the size of the companies you target!