Google blacksmith's coal or farrier's supplies. It contains less sulphur than regular coal.
Most guys have gone to propane. It's easier to get, cleaner to store & doesn't leave clinkers in the bottom of the forge.
Making & tending a smith's coal fire takes some learning & practice. Usually, unless you're in an open area, the smoke & smell from a coal forge starts to offend neighbors & firemen pretty quickly.
Other than the dull roar of a propane forge, there's not much else about propane that will get you the attention of your neighbors or the local F.D.
There's lot's of pro's & con's re. coal, it's definitely classic & more traditional, but IMHO,
propane is more convenient & easier all around.
Larry