I am new and haven't done it myself. But I believe you just use the stemgigs tag and advertise what you want and wait to see if anyone is interested.
For example you can post that you are looking to feature someone who plays in a niche sport and that person will be interviewed and advertised on your blog(s).
It's just an idea, I have no idea if you want to give it a shot or not or even if it will work.
Good luck with what-ever you choose !