Green’s Dictionary of Slang

an independent (record label, film company etc); also attrib.

1928		N.Y. Times 11 Mar. VIII 6: Indies – Independent producers of pictures .
1936		Esquire Sept. 160: Indie duels.
1942		Berrey & Van den Bark Amer. Thes. Sl.
1950		Pittsburgh Courier (PA) 28 Jan. 18/1: It [i.e. a boxing match] will be an indie with Joe [Louis] and Jack [Dempsey] splitting the sugah.
1951		Green & Laurie Show Biz from Vaude to Video 569: Indie – an independent exhibitor.
1959		M. Richler Apprenticeship of Duddy Kravitz (1964) 179: ‘I’m in the film business. An indie.’ ‘I beg your pardon?’ ‘An independent producer,’ he said.
1985		N. George ‘Rappin’ with Russell’ in Buppies, B-Boys, Baps and Bohos (1994) 54: Ex-indie Sugarhill Records [...] once dominated the rap market.
1999		K. Sampson Powder 49: The indies were, often, a bit too reverential, attaching a cultural significance to artistic freedom that their bands didn’t merit.