Charlie Bridger (died 1996) sang 'Darkies' (or 'Playing on the Old Banjo') which strikes me as a period Christy minstrel song. Charlie was born at Kenardington on the fringe of Romney Marsh in Kent, and joined the Woodchurch village band as a boy, retiring to Stone in Oxney in later life. I was given a recording of his songs you still wish to pursue this. Nice polka tune. I may have the words somewhere, otherwise contact me.