Quite impossible I’m afraid. Al Williamson died in 2010. I have no idea who bought or holds the original art.
I wish you luck.
Some company should have it photocopied since they released a re-colored version in the late 90s, not sure though.
Update, I’ve emailed 2 people and waiting on a thirds email address-who were credited on the 1994 version.
update update, there was another re issue during disney’s aquisition so they must have it… emailed 7 people now and also the colorist who did the disney version.