Sponsoring races might work, semi-major ones who have a magazine and you can suggest it to, but that's going to cost (I've no idea on your funding, and don't need to know).
The freeone would be an adverotial type approach in something like Runner's World. They're always desperate for content, so delivering it on a plate (happy for my example to be used) they would probably like. Always free to ask.
Then there is the manual option - hitting all the facebook groups that exist, and the twitter, sugges0ting for all races (likely half and full marathons). You are probably too late for Houson Marathon tomorrow, but that's a good one where people will be in the same position.
Ultimately you are relying on word of mouth, but it's how you get that initial buzz!