Wales, or perhaps the Peak/Lake Districts? I spent some time humping around those as an Army Cadet, you might be able to get them involved somehow - I do recall my detatchment once taking part in a small documentary.
The important thing about fan-films is that they are driven by fans - everyone from top to bottom. My crew will likely be fans. The production team are fans. The cast, both main and extras, will be fans!
The thing that is considered is that first and foremost everyone is able to do the tasks carried out to them. But, at their core, they must be fans - otherwise they are not getting the most out of what is going on, especially since I can't pay them anything. I think I would feel uncomfortable approaching such groups and asking so much of them knowing that they may or may not be fans.
the painting style the artist has used on those paintings is very reminiscent to how i paint warhammer... I'm now thinking of ideas to convert guard into marines....
surely they will fit the marines hands just as well as they do in the game,
think about it, the weapons dont change size when you steal them from you're allies, and the sniper rifle is meant to be huge. i've always had it in my head that it is based off the barret M107 .50cal sniper rifle/anti material rifle which has a fully assembled length of just shy of 5 feet! which is going to look massive in any ones hands!