There's a lot of cam sites that offer pretty good commission splits so you may want to start there. I wouldn't even bother try to selling ad space to escorts or agencies directly unless you have pretty high traffic and stats to prove that it would convert. Sex workers in the know are pretty discerning, and they generally aren't willing any portion of their set advertising budget on anything that isn't a sure bet.
Since you say your website is based in Europe and that the majority of visitors come both from the US and Europe, maybe you focus on tourism in that niche? There have to be some European based cam studios that feature models offering the full GFE, meaning that visitors could book cam shows or just as easily as the 'other' services that may have drawn then to your website in the first place. There are also escorts who sell clips, so you might want to look into that type of affiliate program as well. Just a thought.