The png versions were posted here about 18 months ago:
http://originaltrilogy.com/post/id/959198
http://originaltrilogy.com/post/id/953273
A download link to a zip file containing all of this artwork is available here:
http://www.thestarwarstrilogy.com/starwars/FILES%2F2016%2F06%2FArtwork.zip.axdx
Any newbies wondering what project this artwork was for, can learn more about it here:
http://www.thestarwarstrilogy.com/starwars/post/2016/06/13/Star-Wars-Silver-Screen-Edition-Bluray