For the FBI, I'd contact their Office of Public Affairs. Try the LA office first, before HQ. A public information officer will get you to the right person.
For information regarding FBI Los Angeles' outreach, recruiting, and community events, to include speaker requests, please call (310) 477-6565 and ask for the Office of Public and Congressional Affairs (OPCA) or email LA_OPCA@fbi.gov.
Hope this helps.
Although you should be aware that the FBI's entertainment liaison office--called the Investigative Publicity and Public Affairs Unit--keeps a database of requests from the entertainment industry.