When it comes to such sources and even the lesser known publications like Linking Rings, it really tends to be a political beast; there's a collection of guys that have known one another for some time and they lend support to one another, which makes it very difficult for an outsider to get in . . . difficult, not impossible.
Do reviews for eZines and get your name known; it's going to take a couple of years and consistency. The big issue is that you must have a serious sense of knowledge when it comes to how certain things that are older & similar work; you must be able to filter submissions in order to weed out bits that are basically reinventions of the original wheel -- trust me, there's hundreds of them. Same is true when it comes to the abundance of impractical systems; a prime example of this is CRUSHED which I find to be very impractical for today's market situation but more so, it steps over another line that has seen my wrath more than a few times; I'm talking about how 5th grade level science experiments are being marketed as "new" tricks -- Crushed & Spin are two such bits that I'm aware of, I'm confident there are more.
The other reason you need to have solid knowledge is so you can reference earlier sources and when applicable, name the people and effects that a new release has "borrowed" from.
Being a reviewer means brutal honesty and not pumping hot air up people's skirts. Just because someone gives you a copy of something doesn't mean you are obliged to give it an automatic thumbs up. I've torn many popular pieces a part because of certain shortcomings tied to them. It would not be fare to the people relying on your review, to not know the positive as well as the negative points, especially when it comes to more expensive odds & ends.
Being a reviewer is not an easy task.