Pick 3 custom post id's at random

I am creating a feature on a site where a custom post type (shop-product) has a related items field that allows the editor to select related shop products. If no relations are picked I would like to populate the list with 3 random shop products.

I am using the following code to show the products IF there are relations set:

$relatedProducts = get_custom_field('overrideShopProducts:to_array', 'get_post');
	foreach ($relatedProducts as $p) {
		print_r($p); // this will show you EVERYTHING that's available in that post
		$productTitle = $p['post_title'];
		$productPrice = $p['price'];
		$productImg = $p['mainImage'];
		$img_src = CCTM::filter($productImg, 'to_image_src');
		$productHref = CCTM::filter($relatedProds, 'to_link_href');

		$product_html[] = '<img src="' . $img_src . '" /><div class="indvdlProduct"><div class="title">' . $productTitle . '</div><div class="price">' . $productPrice . '</div><a href="' . $productHref . '" title="' . $productTitle . '">Buy now</a></div>';

	}

My question is, how do I generate something with the same output, only driven by a random selection of 3 shop-roducts? Any help would be warmly received.

Thanks

http://wordpress.org/plugins/custom-content-type-manager/