Found a need with a recent project that had over a dozen custom page templates and the client wanted to know which page templates were in use on which page across the site. So I came up with, get ready for it… another page template. BRAAAM!
You give it a
$templates array of the page template name and filename as key value pairs. It will query for pages with the post meta key
_wp_page_template that match the supplied template name, then display them with links to edit each page.