How can I set up relationship with advertising agencies?

I work as an account executive for a minority daily newspaper in the US. Unlike other A/E in mainstream media, I can very less money. I want to set up relationships with big advertising agencies to expand my network, and eventually draw ads into my newspaper.
I tried so many advertising agencies, but all I had are voice mails and no responses except the front desk receptionist.
My question is how can I reach those people in advertising agencies?
Any advice is welcomed.
Thank you very much.