The required ATF form used to be a form 6 part 1 I believe. Your local FFL dealer can fill it out for you. It would then need to be sent to ATF for approval. Upon approval it would need to be sent back with the gun or it will be seized by customs. What I did was have two german guns shipped back to Dulles Airport via Luftansa. I had sent the approved ATF form to the dealer in Germany and it accompanied the shipment. I also had to have a letter from my FFL dealer advising I was acting on their behalf and I paid the import duty and received the gun. I then took it back to my dealer and then he did the standard FFL form that was required for the Va state police back ground check so they could release it to me. It wasn't that hard, but is took a bit of time to navigate through all the wickets.
