Offhand, I would search for interviews with the screenwriter and maybe director. The DVD extras migh have something, even buried in the commentaries. Finally, the film should have a credited historical consultant, maybe multiple. Check to see who they are, what they've written (if a scholar), and so forth.

Magazine interviews with the costume designer or other artistic crew might get you somewhere. I don't know how you'll fare for something made in 1997, but that's how I'd start. Then I'd look through journal articles analyzing the film to see what might be hidden inside.