FISA Emergency Application : Rule 9
http://www.fisc.uscourts.gov/sites/default/files/FISC%20Rules%20of%20Procedure.pdf
Article with sauce (Atlanta Journal Constitution):
https://www.ajc.com/news/national/what-fisa-warrant/WqP428Eg04nHe933u1GazO/
Is there any other way to get surveillance warrant?
An alternate way a warrant for surveillance can be obtained is if the U.S. attorney general declares an emergency and authorizes the employment of the surveillance. The attorney general must notify a judge on the FISA Court, and must, within seven days, apply for a warrant for the action.