Add feed to a custom page

The only way to accomplish this would be to add in new rewrite rules for these urls. There are a bunch of different ways to accomplish this, but here’s one example:

<?php 
add_filter( 'generate_rewrite_rules', 'me_filterRewriteRules' );

function me_filterRewriteRules( $wp_rewrite ) {
    $newRules = array();
    // Replace [your-slug] with the slug of your page
    $newRules['[your-slug]/feed/?$'] = 'index.php?feed=rss2';

    $wp_rewrite->rules = $newRules + $wp_rewrite->rules; 
}
?>

You’ll need to add a new rule with the appropriate related query strings for each page you’d like to add a feed to.