Let me turn that question around. Why would they want to be on the Executive Committee if they don't want anyone to contact them (by the least intrusive and most anonymous means there is)? Put a motion up at your next AGM that all EC members will display their names and either email address or apartment number on the EC minutes and/or the notice board of the building.
If they don't want anyone to contact them then they are obviously on the EC for their own benefit and no one else's and they need to get off and let more community minded people on board.
Sending someone an email in their capacity as a fellow member of the Owners Corporation is not a breach of privacy. Sending their phone number to all and sundry would be. They need to ask themselves why they stood for election in the first place.