Powerz,
Believe it or not, many journal editors desperately need reviewers. You don't need to be very convincing and find good arguments!
Just tell them your title (should be Ph.D...), affiliation, your field/interest (list a few key words or precise your field), and that you are interested in reviewing articles for their journal at their earliest convenience. I would also attach a short resume.
You probably have published papers in a few journals? You may want to begin with the editors of these journals, since they "know" you.
I also told a few people that I needed to review papers for a green card (though I have decided not to apply for EB1 finally) and then I received emails from editors who didn't even ask for my credentials.
Hope it helps....
