The closest match to "Natural Bodybuilding" magazine is "Natural Bodybuilding & Fitness." According to Get Big, "Natural Bodybuilding & Fitness" is a quarterly magazine that claims to be the only magazine dedicated to a drug-free lifestyle. The editor is Steve Downs, chairman of the World Natural Bodybuilding Foundation.
As of August 2014, Get Big lists the subscription rate for "Natural Bodybuilding & Fitness" as $21.50 for eight issues and the mailing address as 350 Fifth Avenue #3323, New York, NY 10118.
Natural Muscle is an additional resource that publishes a magazine with a yearly subscription rate of $24.95. Its mission statement notes that it is dedicated to natural, drug-free bodybuilding and fitness.
Wikipedia has a more extensive list of bodybuilding magazines that includes "Natural Bodybuilding & Fitness" as well as publications such as "FLEX", "Muscle & Fitness," and "Planet Muscle."