How to check pop under traffic volume of different ad networks?

I'm running some geo-specific campaigns, and want to buy pop under traffic. I need to know which ad network has the largest amount of pops traffic in different countries, so that I can buy from them respectively. E.g. ad network ABC has 100K traffic in US, ad network XYZ has 200K traffic in India, etc.

Is these any way to check for such info? I see there are spy softwares on the market, but they are used to check for the offer details, but not the ad network inventory.

 

Are you looking to buy volume or quality ? most adnetwork are bidding based, which means even if they have 100k traffic for certain geo, not necessarily you can buy all, how much you can buy depends on your targeting and bid you setup, so the information you looking don't think is going to help you, your best bet is signup with some network which you can start with low minimum and do some test and see which one works for you, not necessarily a network which has the highest volume may be the best option for you.