G'day Wayne, I've only ever seen the BBQ briquets for sale I've never used them before. Doesn't sound from what you wrote they would make meat taste all that good.
Simple plain charcoal briquets are not a problem and have no bad odors nor harmful ingredients. There is a type that are sold as "self lighting" that have some sort of petro-chemical volatiles, likely as waxes, in them that I also would not recommend, but the plain ones should offer no issues and barbeque stuff without harming flavors!
On another thought, natural coal often has many inclusions that could be considered contaminants, Sulphur especially, that could stink up your steaming room, so perhaps best to run outdoors when using coal. Sources easiest to access are usually Farriers (horseshoers) or Blacksmith supplies sources, but it typically comes in about 50 pound bags or the like. Maybe you could go online and find your nearest Ferrier or Blacksmith and buy a few pounds from them?