Plug-in that shows x number thumbnails from another post

I don’t think so, but you could use get_children and get the attachment(s) of those posts:

$attachments = get_children(array(
  'post_parent'     => $post->ID, // <- source post
  'post_status'     => 'inherit',
  'post_type'       => 'attachment',
  'post_mime_type'  => 'image',
  'order'           => 'post_date',
  'orderby'         => 'DESC',
  'numberposts'     => 5,         // the number
));

Then get the image URLs:

$size="post-thumbnail"; // or whatever size you need

foreach($attachments as $att){
  list($source, $width, $height) = wp_get_attachment_image_src($att->ID, $size); 
  // echo '<img src="'.$source.'" width="'.$width.'" height="".$height."" />';
}