Lightroom - Select all files with a corresponding stack ID

query.sql

SELECT 
    s.id_local AS stack_id,
    CONCAT(rfl.absolutePath, fl.pathFromRoot) as path,
    CONCAT(f.baseName, ".", f.extension) as filename
FROM AgLibraryFolderStackImage si
JOIN AgLibraryFolderStack s ON si.stack = s.id_local
JOIN Adobe_images ai ON si.image = ai.id_local
JOIN AgLibraryFile f ON ai.rootFile = f.id_local
JOIN AgLibraryFolder fl ON f.folder = fl.id_local
JOIN AgLibraryRootFolder rfl ON fl.rootFolder = rfl.id_local
ORDER BY s.id_local

You do this by opening the catalog as an SQLite database, and then execute this query. It will produce a table with columns stack_id, path, and filename. You can then use this, for example, to create a script that does something with it.

I used this to organise all stacked images into folders, each stack into its own folder. So I just took the resulting table, and used a code editor to transform it into move commands in a batch file. But you can do whatever you want with it.

Disclaimer: make a backup of your catalog before attempting to open it with a SQLite tool of any kind. Although this will only ever read from your catalog, you can never be too careful if your catalog is worth anything to you.