First you need to think about what magazines you'd like to be published in then think about what you can offer them. There are not many that are going to be interested in a single landscape shot, maybe /out/ type magazines. You'd have a better chance with a photo essay but you need a specific theme and 15-20 varied, and very good, images for that.
And remember, a reputable magazine will pay you for it. It won't be much because their own profit margin is wafer thin but you should never do it for free.