>>How many female kingsnakes do you all think a single male kingsnake can successfully breed (fertilize) to in one season?
You asked for experiences, so i can't address possibilities in the wild--other than to say that, given sufficient female population, i don't see why it might not approximate the possibilities in captivity.
In captivity, based on experiences more with Lampropeltis triangulum than getulus, I'd say an average condition male, brumated (because that's my experience), could reasonably be expected to cover 7 or 8 females. That number takes into account management practices--not leaving him for hours or days with each female, for example (your question really is, or should be, "how many copulations with adequate insemination can a male..."
because if left with a female he might copulate three or four times in a 24 or 48 hour period. Because a single good insemination can produce a clutch of fertile eggs, more than one copulation might be considered "excess" or at least would reduce the number of times he could cop/insem other females. (note that in the wild there's not that management intrusion, so a male might spend days in the same spot as a female, cop'ing repeatedly with her. Only if there was a large female population, causing him to encounter multiple females in short notice, might he father babies with as many females in the wild as he could in captivity.
btw the garter snake guys might know more about this: those breeding masses i've read about (not observed personally) certainly have an abundance of females. (on an only slightly related note, a substantial percentage of goldfinch nests contain babies with a single mother but different fathers. So in a wild environment with a high female kingsnake pop, there'd presumably be numerous males, too, thus i'd hypothesize many females would be inseminated by more than one male.
cool topic.