You can simply include a custom search function into your search by using pre_get_posts
You can do something like this
function search_filter($query) {
if ( !is_admin() && $query->is_main_query() ) {
if ($query->is_search) {
$query->set('post_type', 'your-custom-post-type' );
}
}
}
add_action('pre_get_posts','search_filter');