You can download the reporting form from the internet and print it out at home to have it ready. We fly out of MSY, where there is never anyone there qualified to accept the form and where, when asked, people react with such puzzlement that you feel you've been a little unfair to set them such a hard question. So we have to find out where to drop it off at the airport from which we are actually departing the country. Once at DTW there was also no one there from Customs to take the form. The gate agent accepted it and said that they would get it to Customs, and that my companion (the one who actually had the cash) could go ahead and board. They would let the Customs agent board if he decided to actually show up and ask any questions. No such agent ever presented himself so I assume the form was filled out to their satisfaction. Either that, or Customs was taking the night off.
I would never wait and hope to pick up the form at the airport. It relies on a Customs office being open, the Customs agent being there and ready to deal with your paperwork instead of something more urgent, and so on.
I've complained about this issue before. It's pretty straightforward and someone is always there so that you can report when returning to the United States, but they make it very difficult to properly report when exiting the United States. Since the requirement is to report coming and going, I wish Customs would make it a little easier for honest people to comply in both directions. We shouldn't have to run about like rats in a maze just to drop off THEIR paperwork.