How to find larger advertisers?

Now that DaniWeb is getting bigger, I am targeting more of the bigger budget advertisers. The problem is, how can I find them? It doesn't seem many of them post on many of the webmaster forums such as here, SitePoint, etc. Or do they? Where do larger-scale companies look for advertising? Would it be in my best interest to make deals with the ad agencies that represent them? How can I do that? Sorry for throwing you all these questions at once.