A draft article I’m working on goes into selling of marijuana illegally, whether in violation of prohibition or of tax laws. Under legalization, bootleggers, adept at violating prohibition, commit a new and different crime: tax evasion. But the cat-and-mouse game of enforcement against bootlegging is pretty much the same, whether the crime is violating prohibition or cheating on taxes..
Several readers object to the term “black market,” on the theory that it has racist origins. Maybe that’s accurate. Either way, some say it disparages Black people. So I’m steering clear of the term. Words are here to serve people; people aren’t here to serve words. Cf. Mark 2:27. (I’ll keep using the derivative term “gray market,” or grey market, referring to transactions like a patient’s selling legally bought medical marijuana to a recreational user.)
Illegal market, unauthorized market, illicit market – they all take more space and syllables than their predecessor. What’s the opposite of punchy? So I struggled for a substitute.
Bootlegging (origins obscure) is it. Three syllables. The permutations — bootlegger, bootlegged — are as short as the old terms or shorter. And they’re punchy.
The Center for New Revenue 
Here in California many of us like to refer to what you call “the grey market” as “the free market” which I prefer because of the high dispensary prices and outrageous taxes adding up to 34% on legal purchases in Los Angeles. Slightly less for medicinal purchases.