Ask yourself this: Why would YOU want to guest post in another person's blog? If the blog has quality content, lots of traffic and lots of followers, you'll want to post there. Go and do the same. Good luck!
If you haven't already, announce on your blog that you're open to guest posting. Give them an incentive to guest post, maybe some pay, or some type of special promotion or free mentoring session. The more attractive you can make guest posting on your site, the more likely you are to get pitches in your inbox. Happy Blogging, -Brian