My tactic has always been to go in and speak to whoever mans the office, receptionist/pilot. Treat them like you are delighted to get a chance to speak to them and would they please pass on your resume/details to the relevant parties.
Many companies use the office person as a gate keeper. You won't get past them until the CP wants to see you, if you treat the gatekeeper right you go a long way to getting to see the CP. Some companies will let you meet the CP (usually a hand shake and basic introductions) straight away but it still doesn't hurt to make a good first impression; you may be seeing that office person every day you rock up for work in the future!
