Cape Town has one dedicated queer shop, and it's in the gay village. Rainbow Nation at 14 Jarvis Street, De Waterkant, calls itself Africa's only walk-in queer lifestyle store. It sells Pride flags and accessories, locally made clothing, books, gifts and souvenirs. Google lists it as open Monday to Saturday from 10:00 to 18:00, and it also sells online at rainbownationshop.co.za.
Rainbow Trade, the older De Waterkant shop, has closed. The adult stores you'll find around town, including the Adult World chain and Olivia Grey in the Cape Quarter on Somerset Road, are mainstream shops rather than gay ones.
For everything else, the Cape Quarter and Somerset Road are a short walk away, the V&A Waterfront has the big mall, and the Old Biscuit Mill in Woodstock runs a busy Saturday market. Cape Town Pride in February brings pop-up markets of its own, so check the programme on cptpride.org if you're in town then.