Generating Advertising leads from bigger companies

Our main website currently receives 1.5 million visits... and generates about 14 million banner impressions in each of 3 banner zones, a month. The website consists of nearly 2000 pages of content on everything to do with sexuality... and a very active forum. Traffic is international, but most dominant in english speaking countries... especially USA, UK, Canada and Australia. We have a licensed in house ad delivery system (pretty advanced), but we are considering switching to Google's Double Click for ad management. We have had difficulty in breaking through to some of the bigger advertisers that you would think would jump at the chance to promote their products on our website... examples: Durex, Trojan, Axe. The leads to not have to be for giants, but we deal with enough small accounts already. Although we've discussed a number of models on how to best implement a freelancer position in this role, we haven't come up with one that covers all the concerns... Would it just be getting the lead... would it include converting it... supporting it... etc.... these are things that we would need to be figured out. We are also open to this person becoming a member of our team. If we can find an ideal candidate, we are willing to pay the $99.95 upgrade for the full time position to reduce the middleman fees.