What I have understood is,
User Story:
As a user I want to search for specific item and get the nearest store information.
System Flow:
First locate the user location using Google Map API. So when user at
your APP you need to check if this Device is connected to internet
and GPS is open. If not, ask user to on it.
Get the nearest store based on the user location. If your database
is in Web, you need to develop an API and send the User Location as
Parameter [There might be other parameter based on your API set up
and requirements].And, return the Store.
Get the Product details of the Nearest store and show to the
user.You need another API here to get the product details. Develop
Another API and pass the Store name / ID as Parameter at this API and
return the Store product details.
So you need another 2 API (RESTful API might be easy and faster).
First API will rerun the Store and second API will return the Store
Product. From your App you need to call / consume the API.
Hope this will help, if there are any other difficulty to define the process and Flow, feel free to ask.