Custom button on custom taxonomy listing page

This action hook (found in /wp-admin/edit-tags.php) will output the button below the table (not quite where you have asked to position it, but it is an easily available action and outside the form table.)

$taxonomy = 'location'; // you will probably need to change this
add_action('after-{$taxonomy}-table','custom_export_button');

function custom_export_button($taxonomy) {
    $export_url = admin_url('admin-ajax.php').'?action=export_taxonomy';
    echo "<form action='".$export_url."' method='post'>";
    echo "<input type="hidden" name="taxonomy" value="".$taxonomy."">";
    echo "<input type="submit" value="EXPORT"></form>";
}

add_action('wp_ajax_export_taxonomy','custom_export_taxonomy');
function custom_export_taxonomy() {
    // YOUR CUSTOM TAXONOMY EXPORT FUNCTION
}