It isn't uncommon to find Corn Snakes anymore, I have found them and plenty of people I know have found them. The only uncommon thing to find is a naturally coloured one, they all tend to be various forms of albino. There are literally tens of thousands of them being owned, I doubt many are being bought into the country anymore as there are thousands being bred in Australia each year. They are cheap to buy, very hardy and placid snakes, ie ideal to keep. The vast majority of people who keep them arn't on the native animal licence sysytem and don't care about it, they know there is only a slim chance of getting a slap on the wrist for having them and most of these people have done worse anyway, thus don't really care if it gets confiscated, easy enough to buy some more.
As for the moral dilemma of euthing it??? well... it's a bit like going up to Qld and killing 1 toad... thats how it stands atm anyway, I hope the authorities take a harder stance on this trade but I'm not holding my breath for it.