Green’s Dictionary of Slang

(US drugs) a drug dealer.

1937		B. Dai Opium Addiction in Chicago 203: Shover. A drug pedlar; and as in ‘So-and-so is shoving’.
1942		Berrey & Van den Bark Amer. Thes. Sl.
1950		Goldin et al. DAUL.
1953		Anslinger & Tompkins Traffic In Narcotics 314: shover. A drug peddler.
1978		W. Diehl Sharky’s Machine 234: Red devils, hunh? [...] Lemme see, that could be, you know, three or four shovers I know of. Gimme an hour.