When you commence production, place an article in 'Railway Magazine' - many preserved railways would probably be interested to learn of real steam coal becoming available from a UK source; transport costs to the various south Wales lines would surely make it more attractive for them than more distant lines, so letters of flyers to them might be useful too. I was talking to the staff at the Waterfront Museum in Swansea when they were steaming their replica of Trevithick's 1804 Penydarren Locomotive last year; they said that when they finished the decidely elderly remmnant of coal they had in stock, they didn't know where they would get more from, and worried what grade they would obtain. So there's one potential purchaser, albeit for very small and infrequent quantities.