I have an almost unlimited quantity. The banners will be served on the www.exchangead.com network. If you interested please contact me at [email protected] (Disregard the xxx it protects me against spam)
I know someone who used a million of his banner impression credits in a day. That gives you an idea of how large the network is ( I don't own it). I don't have stats on members or demographics.
If you would like I can set the banners to be concentrated in a specific category such as games or computer related.