In Britain the answer might be at ASDA, Tesco, Waitrose, Sainsbury’s, Morrison’s, Marks & Spencer’s, Debenham’s, Harrod’s …
But some would say “Tesco’s”, and I’ve also heard “Waitrose’s”.
The ‘regular’ treatment of shop names is to add the genitive to a family name (i.e. ‘Mr Sainsbury’s shop, Mr Morrison’s shop’ etc.), but not to a company name that is not originally a person’s name, so “at ASDA” (an acronym from “Associated Dairies”.
Tesco and Waitrose also come into the latter category, Tesco being an acronym from “Tessa Cohen” (the founder’s wife), or perhaps from “T.E.Stockwell” (a tea supplier back in the 1920s) and “COhen”, and Waitrose likewise being an acronym of two of its founders’ names (Messrs Waite and Rose).
Increasingly, however, the ‘rule’ appears to be breaking down. Not only is “Tesco’s” frequently used, and Waitrose starting to become “Waitrose’s”, but there is real uncertainty about how to treat the newer budget supermarkets that have come in from Europe – Aldi, Lidl and Netto. On the other hand, does anyone shop at “John Lewis’s”?