Frances Wright (1821). “Views of society and manners in America: in a series of letters from that country to a friend in England, during the years 1818, 1819, and 1820”, p.518
"A Note on the Theory of the Black Market" by Kenneth E. Boulding in "The Canadian Journal of Economics and Political Science", Volume 13, No. 1 (pp. 115-118), www.jstor.org. February 1947.