My experience is there is no Ryhmn or Reason to where you will find them.
I generally try the 450-470 band, not skipping what would generally be inputs, as they do use them simplex.
Some finds of mine and others over the years for New England are at:
Movie Productions - Scan New England Wiki
IF you can't find them in UHF, you might try VHF, but already knowing what is in use can help
As I've found them on active business channels, that normally I might lock-out, but knew it was a different PL/DPL than my regular find.
Good luck with the hunt, and if a major production, expect multiple channels.
Production, Electrical, Talk-Around, Set Construction, Transportation, Food Services, Wardrobe etc
There is a movie fliming in my area and I cant find frequencies