Q. Retail sales: statistics

Search Passport for data and country reports supplied by Euromonitor for many countries.

One can search for statistics (and reports) on broad categories such as Retail sales or specific categories such as Footwear. 

Go to Statista

Also, you can go to Eurostat or go to U.S. Census: Retail Trade for U.S. data.

See the Global Retail Development Index (GRDI) published by A.T. Kearney.