Earlier quoted context omitted.
The bigger point is that journalists usually need to go back and forth with you.
Tell the reporter to mail you at Mailinator or Lockbin.com and retrieve their messages by connecting with TOR.
The communications from the reporter don't need to be private or targeted. Everyone will know he's involved when he publishes, and he can reasonably encode questions by referring to the documents already sent. "MR X, CAN YOU PROVIDE FURTHER INFORMATION ON THE EVENTS DISCUSSED ON PAGE 13."