<?php
	$args = array(
	'order'          => 'ASC',
	'orderby'        => 'menu_order',
	'post_type'      => 'attachment',
	'post_parent'    => $post->ID,
	'post_mime_type' => 'image',
	'post_status'    => null,
	'numberposts'    => -1,
	);
	$attachments = get_posts($args);
	if ($attachments) {
	    foreach ($attachments as $attachment) { ?>

	    <?php echo wp_get_attachment_image($attachment->ID, 'large', false, false);
		}
	} 
?>

Solution - 1

Change:

echo wp_get_attachment_image($attachment->ID, 'large', false, false);

echo '<a href="'.wp_get_attachment_image_src( $attachment->ID, 'full', false, false ).'"><img src="'.wp_get_attachment_image_src( $attachment->ID, 'large', false, false ).'" alt="img" /></a>';

Solution - 2

Not familiar with Thickbox, but if you want to add a href around the image: The new loop would be:

foreach ( $attachments as $attachment ) {
	$full_image = wp_get_attachment_image_src( $attachment->ID, 'full', false, false );
	list ( $full_src, $full_width, $full_height ) = $full_image;
	echo '<a href="'.$full_src.'">';
	echo wp_get_attachment_image( $attachment->ID, 'large', false, false) );
	echo '</a>';
}

Solution - 3

//Put images from post in to array $images. Order by menu order defined in post gallery
	$images = get_children( array('post_parent' => $post->ID, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order ID') );
	if (isset($images)) {
	$count=0;	
	//go through all images in array $images
		foreach( $images as $image ) {
			$imageID = $image->ID;
			$medImageSrc = wp_get_attachment_image_src($imageID, $size='large', $icon = false);
			$largeImageSrc = wp_get_attachment_image_src($imageID, $size='full', $icon = false);
			echo"<a href='$largeImageSrc[0]' rel='thickbox'><img src='$medImageSrc[0]' alt='Image' /></a>";
			$count++;
		} //foreach
	}