Flames of war has a line of 15mm that can work. They do have some Korean Conflict stuff. Shapeways has some "George Pal Movie" Martian Machines. If you look close, the floating machines have three ghostly legs.
you could also use a lot of World War II stuff. Tons of that stuff was sold to foreign countries after the war. Not to mention a lot of it staying behind. This could lead you to building some very interesting armies and changing the storyline to different locations on the planet!