That sounds interesting, may be something I am interested myself or can help directly. With that said, I don't want to spam or pitch, so let's see...
Based on my experience meeting with clients and having done some projects and appeared on television shows I can say that a lot of the advertising business developers work mainly off networking in person. Relationship building for pipeline building. Obviously, as marketer, I think there are better more efficient ways but networking, in my opinion, will always be the cheapest and easiest and in some cases the most effective.
What you need is a funnel system with case studies and examples serving as ads for your own end goals which is to sign up brands. Partner with potential vertical companies that can help you sell spots more regularly such as established ad agencies and magazines.