They're called Tandy. They certainly used to sell a number of parts marked 'radio-shack'.
I haven't seen a store for years actually - I don't even know if they're still trading. I never bought anything from them, as they were grossly overpriced and sold nothing of use (apart from some low quality CB kit, and music equipment). The staff were also invariably clueless, despite a massive advertising campaign about how knowledgable their staff were, and how they prided themselves on answering your questions.
Maplin is probably a better comparison - they sell a wide variety of stuff - from consumer or more eclectic electronic devices, PC parts, DJ type equipment, and individual electronic components and development equipment. They are very expensive (ludicrously so for computer equipment), but have a relatively efficient mail-order service and a website that works (albeit not very good), as well as numerous high-street shops.