Since Amazon Mexico already sells food, that would be the only way to get groceries in small towns. But supposedly they sell through JUSTO in other towns. The only way to know is put the zip code of the city in the shipping/location field to find out. Since it's a new service, new delivery locations will be added as time goes by.

Here's the bloomberg report:
https://finance.yahoo.com/news/amazo...160000159.html

Here's the Justo link in Amazon Mexico:
https://www.amazon.com.mx/alm/storef..._=nav_cs_justo