From my experience, PopAds got the best rates for every country (unless you can manually find private advertisers), I had a $3.5+ CPM for Israeli traffic (Which is crazy good).
PopAds.net is your best bet. Why don't you try a reputed banner network that also offers pop under ads? From my own experience, pop under ads from reputed networks like Adversal, Fidelity Media or PropellerAds perform much better and also you can be assured to receive timely payments. This might help - http://adsreview.in/top-5-cpm-banner-network-which-also-offer-high-paying-pop-up-pop-under-ads/ ~ Remya. EDIT: AdOnly is another one that offers highest rates for Asian traffic.
For the popunder ads PropellerAds media is the best place. They are offering highest rate for popunder ads. you can get around $2-$3 per 1K impression.