Speaking from experience, the longer you're on Youtube and the more videos you post, the better chance you'll have of companies finding -you- and emailing -you- about having their products to review.
A couple tips I have:
Always have a contact email both on your Youtube channel itself as well as in the description of every video.
Contact small, lesser known off-brand accessory companies. Look for cheaper phone case manufactures or powerbank/phone charging distributors, especially Chinese companies and particularly on Amazon. Email the sellers of all of the top ranking cheaper phone cases on Amazon. Look up the best selling powerbanks under $50 and try them. Search for some other types or phone, tablet or smartwatch accessories like stands, chargers, screen protectors etc. and start there. It isn't glamorous or exciting, but its a start.
You aren't going to get companies like Motorola, LG, Samsung or any other big names wanting to give you products for a long time. But a lot of little known, off-brand overseas companies will send you products even at 100 subscribers.
Like anything, it takes time and commitment. There's no shame in sending out 100 professional and well written emails to any companies you can think of and not getting any replies back. But the 1 company who does end up replying back might be someone who you can consistently work with. Be patient, persistent and professional and upload consistent content and eventually companies will start coming to you.
Wade
TechDaily