The buses are toy die cast metal and I got them at Jewel Osco for $6.00 each, can you believe it?
They are made in China and are real close to 20 mm so they would be to small for 28 mm.
Take FATROC's suggestion and look on e-bay.
The wire mesh is easy. Go to Lowes or a hardware store and look for a roll of fiberglass screen window for $6.00. It comes in a roll about 3 feet wide plenty to do anything you can imagine a use for. I was planning on trying it to make chain link fence but for 20mm it may be to big, not sure yet. For 28 mm it will probably do just fine.