Go to a judge and get a warrant like actual criminal investigators do every day.
Screw the Justice Department.
Take them out of the loop. Don’t tell them a damned thing either. When you’ve got a case, take it to a court and try the case.
I am not sure, but the FBI are the investigators, and the DOJ are the prosecutors. This needs to go till after January to get this prosecuted...unless there is a pardon.