I'm always on the lookout for how agencies get into companies. Here's an approach I heard from an IT staffing firm:
"Hello, my name is X, we've done business with you in the past through our sister company Y who does temporary office staffing. I was wondering if you have any needs in the technology arena or could direct me to someone in your company who makes those decisions?"
If you are that person, the agency then said this to set up an appointment:
"Well, I always found that it is helpful to set up a meeting before actual needs develop, would you be open to a meeting sometime?"