Posting on other company's/people's blog/magazine?

[Vlady]

I recently started working for a clean energy start-up that locates energy incentives and tax rebates for commercial and residential utilities. My work entails managing all aspects of marketing for the company. As of now, we have a Twitter, FB, Linked In, and Tumblr account for reaching out to potential customers. My boss approached me the other day and asked if I could find a way to write articles on other green blogs or magazines promoting our company. I'm not entirely sure if this is possible seeing as how most blogs or online magazines have their own staff of qualified writers. Any suggestions would help. Is this even possible? Is posting on forums an alternative to this?