One thing you can try is to seek out publications or blogs that are known, then try writing for them. If you get known on that site as a critic, then you’ll end up eventually getting promos.
I will say though that to get the newest/coolest stuff you have to be well-known. The idea of promos is that you’ll play it, other DJs and consumers hear it, then run out and buy it. If you’re not able to reach loads of people easily, then they won’t give you freebies to help them promote music.
I get some promos…but I’ll be honest most of them is stuff I’m just not into…so I’m out shopping for music anyway. I’m also just a fan of buying music so I support the producers I like.