If a company is not interviewing on campus, it doesn't exist. This is obviously an untrue statement. Yet this is the unconscious job search approach of many college students who attend the on-campus job fair, then take their five or ten or twenty on-campus interviews, cross their fingers and hope something happens. And in doing so, the entire job search universe has been restricted to only those companies that come to campus.
There are far more companies out there than those that are visiting your campus. To fully maximize your job search, consider all companies as potential employers. Reaching out beyond the campus bounds requires more effort on your part, yet the payback is considerable. In addition to increasing your overall odds of finding employment, you are also increasing your odds of finding the right job with the right employer.
Signing up for on-campus interviews is relatively simple, while it often requires a great deal of effort to penetrate the armor of a company that is not interviewing on campus, especially if you have no internal leads or contacts. But keep in mind the potential rewards in pursuing off-campus employers. You have the opportunity to target specific employers in specific industries in specific geographies. Simply put, it is proactive job search by design, rather than a reactive job search by default.
Getting through to a key contact should not be a blind shot in the dark. This is an exercise in quality contact, not quantity. It doesn't matter how many arrows you shoot if none of them hits the mark. After all of your preparation to date, make sure you drive home your point by aiming for the right target.