WordPress | Get URL from page template name

url_from_template.php

<?php
// Get the URL of the first page using a specific template
function url_from_template( $template_name ) {
    $args = array(
        'post_type' => 'page',
        'fields' => 'ids',
        'nopaging' => true,
        'meta_key' => '_wp_page_template',
        'meta_value' => $template_name
    );
    $template_pages = get_posts( $args );
    if( $template_pages ) {
        $first_id = reset($template_pages);
        $permalink = get_permalink($first_id);
        return $permalink;
    } else {
        return null;
    }
}
?>

This, ever so slightly extends this gist.