I am also looking for it, but have not had any luck so far. :( It's my personal holy grail in SW-artwork. ;)

What's interesting is that the droids were actually added by comic book artist Nick Cardy, apparently he also added little details to the other characters, the same last minute touch-ups were also made on Jung's half-sheet, don't know if it was from the same uncredited artist on that though, they look quite different, and IMO don't fit with Jung's art at all. The original half-sheet art is on the cover of the 1977 theater-program, I will scan it someday.

The Hildebrandts were also told by Lucas to add the droids on their Tom Jung variant in the last minute, that one I have though.

If you don't find it, maybe a little photoshopping will suffice, but it doesn't feel right. ;)