Green’s Dictionary of Slang

(Aus./N.Z.) a second-hand clothes shop, thus attrib.

1943		Williamstown Chron. 10 Sept. 3/3: Our branch raised the sum of £245/17/. [...] Proceeds of entertainments, £107/6/2; sales of badges, £51/12/5; sales and donations at kiosk and opp. shop, £57/18/3; sale of stamps, £19/15/2; donations, £9/7/.
1950		Sydney Morn. Herald 16 Feb. 10/3: [T]he braln-wave of the ‘Op. Shop’ to stage a mannequin parade of second-hand clothes in aid of the Peter Pan Kindergarten.
1966		Western Herald (Bourke, NSW) 18 Mar. 3/4: The Opportunity Shop is still a steady source of income [...] Any article you don’t need please send to the Op. Shop.
1979		Victor Harbor Times (SA) 4 Apr. 24/3: Wednesday, 28 March, was the opening date for the ‘Little Op Shop’ in Yankalilla [...] Anna and Ann would appreciate any donations of second-hand clothing and articles for the shop.
1986		R.G. Barrett Real Thing 61: An old, grey, op-shop gaberdine overcoat.
1988		McGill Dict. of Kiwi Sl. 79/2: op shop opportunity or secondhand shop, often selling clothes cheaply.
2003		McGill Reed Dict. of N.Z. Sl. 149: Opportunity shop, selling secondhand goods cheaply. ANZ.
1989		B. Reed ‘Messman on C.E.’s Altar’ in Passing Strange (2015) 17: Messman was able [...] to find a very special [...] St Vincent de Paul’s op shop open.
1998		R.G. Barrett Mud Crab Boogie (2013) [ebook] The blokes dressed much the same — op-shop clothes, army disposal gear, Van Dyke beards and John Lennon glasses.
2006		B. Matthews Intractable [ebook] [M]ore often than not she turned an op-shop cast-off into a Gucci original.
2015		G. Disher Heat [ebook] Trask glanced around at the other paintings: community art fair gumtrees and op-shop horsemen droving sheep.
2018		C. Hammer Scrublands [ebook] The op shop is open, a rack of clothes placed out on the pavement.