Good lead. I found some black aquarium gravel at My Fish place that was exactly the same size as Lionel coal. Purchased like a 5 lb bag for $2.99.
For ballast I use crushed gravel (sold as chicken grit), toss some dark gray latex paint in it (if needed) , stir thoroughly and put it near a heat duct register to dry for a few days. You can buy it at Tractor Supply and its economical.