^Ack, I have been out-Google-fu'ed! Congrats on finding a larger version of that Bibi Besch cover.
Okay, so we've located the originals for the Pike and Enterprise
images on the Children of Kings
cover and the Carol Marcus image on the Inception
cover -- that leaves Kirk, Leila, and two Spock images to track down. Shouldn't be hard with the Inception
images, since we know the specific episode for Leila and for Kirk in that uniform, and Spock is from one of the two pilots. But the Spock on the TCoK cover should be the tough one.
EDIT: Okay, here's Kirk, from the scene in "Where No Man" where Gary was in the cell on Delta Vega:
Spock, from near the end of "The Cage" (just after Colt and Number One beam back up):