I'd suggest a similar approach as csallen, though Step 1 should probably be to do research to find similar newsletters, websites, magazines and find out who is

I'd suggest a similar approach as csallen, though Step 1 should probably be to do research to find similar newsletters, websites, magazines and find out who is advertising in them. Once you know that, you will have a much better idea of who specifically is currently spending advertising dollars (display or affiliate). Knowing who is spending money already is really important because getting companies to carve out some of their existing budget for you is easier than getting companies to create a budget out of thin air for you.