This is a timely subject. While not modeling a junkyard scene. I do model the WW2 era and haven been thinking of doing a scrap drive. Even started researching it this week. I've seen a few pictures on the internet where piles of tires were placed right downtown to be picked up.
One site not mentioned. www.rustyrails.com they offer a few tire piles and many assorted junk piles.
Mike,thanks for the heads up on DieCast Direct. Never thought they sold individual tires. Reasonably priced to.