The supermarkets along the border here in the ore mountains absolutely suck, they’re all some ‘duty free’ type shops for the Germans coming over the border to buy something cheap.
i do believe that lot of people living in the border regions actually go for their groceries to germany, it may be cheaper and have better quality. but you will find something in every biggre city, just don't be on the main road. google maps should give you list of grocery stores. there are also local mapy.cz which works very nice, both of them (google maps and mapy.cz) have ability to download maps for offline use when you get to wifi somewhere.