edit - if you see some on the various ebays around the world, it may be worth asking if the sellers would be willing to do you a hi-res scan for you? - and maybe offer them a few $s for their troubles?
there is one on the uk ebay now if interested? - http://www.ebay.co.uk/itm/Star-Wars-Episode-III-Revenge-of-the-Sith-Rare-Collectible-VHS-Video-Tape-/122412501609?hash=item1c805a8a69:g:UgUAAOSwsW9Y1Bed
It turns out the seller of that Episode III VHS tape on ebay is a member here - who has that VHS tape for sale as a listing in the ‘Memorabilia Discussion and Buying/Selling/Trading’ Section on here - it may be worth asking him if he could do you a hi-res scan of the cover for you?
Ah you see he’s in the UK. I’m in the US. But I’ll go and ask for a scan.