Who should I be talking to at a company when pursuing sponsorship?

Focus your energy on decision-makers, not the easily approachable people at ground level. The tire engineer at races or the trade show booth staff won't sign checks or approve sponsorships - they might put in a good word, but they're not the right target. Do investigative work to find who actually makes sponsorship decisions. If you're building relationships with field staff, ask them directly: 'Who heads up your marketing department? Who's in charge of sponsorships? Can I get their contact information?' Then pursue face-to-face meetings with those decision-makers.