Here's the site of a friend of mine from Brazil, he has some cool tips.
Here's a page of a guy that does some great small dioramas.
Some time ago I had picked up some small diecast armor at Wal-Mart for only a couple dollars each, the detail wasn't too bad, not sure of the size but I would guess around HO? I never thought of it back then, but they would be great for small dioramas like this and if they are close to HO scale, it would make finding accessories and figures a lot easier. I'll have to see if they still carry them, I have no idea who made them anymore though.