black market 
noun
An illegal traffic or trade in officially controlled or scarce commodities: the men planned to sell the meat on the black market [as modifier]: black market currency trading...
- Keeping drugs illegal not only costs billions in enforcement, but loses billions in tax revenue by keeping the drug trade a black-market affair.
- Investigators concluded that the colonel enlisted his men in a black-market currency scheme that netted him tens of thousands of dollars.
- But like drugs, and alcohol during Prohibition, black-market contraband always provides a means to acquire whatever is the forbidden fruit of the moment.
Derivatives
black marketeer
- The media like to paint it as a rather wild place, full of black marketeers, mobsters and an amorphous group of people they mysteriously call the ‘Mafia'.
- Fortunately, he had anticipated trouble and had made arrangements for black marketeers to smuggle out the footage he already had.
- The author tells us it is simply a matter of supply and demand, with nuclear black marketeers actively establishing connections between likely end-users and would-be sellers.
black-marketeering
- There was a widespread popular anger sparked by high prices (these had more than doubled during the war), a scarcity of goods, and black-marketeering.
- Food rationing together with spasmodic black-marketeering for tea, meat and the like persisted until I was seven.
- It also would serve as a propaganda ploy to show that the government was fighting high-level crime and black-marketeering, opponents say.