The best way to approach this is to ask for the person who handles buying X (with X being whatever it is that you are selling). I sold millions cold calling using this approach. That said, expect lots of roadblocks and some very difficult gatekeepers. Ask for the person's name and email address, or leave a brief, upbeat voice mail if you are lucky enough to get patched through to the right person.
Follow-up your voice mail with an email in a day or two and some new info. Make a note to check in with the contact in another few weeks, and know that it typically takes up to eight tries before you might actually get to speak with the right person. Patience, gentle persistence and professional, enthusiastic interaction will help the process along.