My company needs blog posts with longtail keywords that drive in bound leads to site. Looking for someone with the experience.
There are a number of blog writing / content creation & management resources: Zery's, ion, Ceros, Kapost, for example.
However, your best bet is to handle this process in-house on behalf of your clients. Use LinkedIn to connect with freelance writers. Your best results will come when you can partner with a freelance writer who has a basic understanding of the topics you are looking to have covered.
Let me know if you need any more guidance. I've operated an agency for 15+ years and now consult on the topic of running an agency (specifically outsourcing such tasks).