You should definitely try Plugrush.
We have blind traffic and popunder traffic, which is what you seem to want to purchase.
We also have what we call plug traffic, which is clicked traffic to your specific ad. If you're looking to get signups, this type of traffic should perform better than blind traffic.
You can narrow it down by sources (i.e. from tubes or blogs) and of course by geographical location as well, which you should definitely do depending on the product(s) you're selling.
If you have questions, don't hesitate to contact me: sascha at plugrush dot com