I'm not sure if the blacksmith was making his own charcoal, or exchanging the wood for charcoal from someone who specialized in that. My Dad's village was about 250 km from this village [1] where people make charcoal even these days (one of the last remaining charcoal burning sites in the world). It's possible back in the day there were much more numerous such sites, so one would not have to travel far.

But even if they had, trade over large distances was surprisingly common. When I was a kid and spending summer vacations on the countryside, my grandparents were involved in a business of selling timber that was felled in some forests about 500 km away. The lumberjacks would bring the logs during the summer months, lots of it (maybe hundreds of cubic meters), and my grandparents would sell it to whoever needed it throughout the year. This was happening during Communism, so I guess it was some form of under-the-tables Capitalism at work. I imagine similar arrangements existed throughout the Middle Ages.

[1] https://wanderingcows.wordpress.com/2014/05/02/the-charcoal-...