If you're using the frontend filter for the dropdown, then you won't be able to use the shortcode attribute as a filter.
Given the care you can pass the values in the URL separately but not through shortcode attribute.
Checking back your initial thread "Scotland, Wales & France" seems to be a part of the same filter that has the other locations. Taking this into consideration we won't be able to use this filter to only show all the others except those 3.
The best option I can think here is to add a distance filter or use some other criteria that would be unique to the locations that you want to appear.