Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Graphics and Visual Effects › Creating a battle scene › I’d echo McRockett’s comments
I'd echo McRockett's comments. In the US, there is an active community of Civil War re-enactors, and I suspect there are probably English and German re-enactors for the Seven Years War. If you can find them, you could probably get permission to film at one of their re-enactments, or they may be able to lead you to stock footage that already exists.
If you aren't already involved in video production, you'd probably be happier hiring someone else to edit the footage and put a finish on the film. You could probably get a short film done for £3,000 to £5,000.