A Correspondent turned me on to the iTMS Album Artwork Finder. It displays the 600 x 600 px album artwork for any cover art at the iTunes Music Store. Simply right-click or control-click on the album art shown for an album at the Store and select "Copy iTunes Music Store URL". Go to iTMS Album Artwork Finder and paste the link into the form. In a few moments you get the big ol' artwork. Not always fruitful, depending on the kind of link you enter. Works best with the link from the actual album listing's album art, as in this snap:
Source >>