If your document is structured into a table with shop/product in separate columns you can do the search in one step.

If your document is structured as you showed then you need to sort the products for each shop individually and then make sure the shops are formatted with a built-in heading style (or more correctly, with an outline level), change to Outline View, show that level of outline and select and sort the headings.

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Andrew Lockton
Chrysalis Design, Melbourne Australia