Hi!
We would indeed be interested in buying your display inventory. We have a sales presence in US, UK, CA and AU and we could sell your 728x90, 300x250 and 160x600 ad sizes. We would however have to work on individual sites opposed to working on RON basis.
If you thing we can collaborate add me over Skype at arshad_uberad or email me at arshad@uberadmedia.com

Cheers!