Most people do their western food shopping at the "Mega" stores such as Emart, HomePlus, Homever, and Megamart. These carry stock items that you aren't going to find at the ma and pop joints. There is also the Asia Mart, a specialty store in Sasang, that carries all you need to cook Indian/Pakistani dishes.
There are also a lot of foods in the Gukje Market in Nampodong.
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