I've always been interested in this sorta thing. Highly organised, illegal activities have existed in almost every culture on the planet like a social undercurrent. Drugs, counterfeiting, smuggling..
In terms of exotic herps, from what i have heard and read, try asking any biker friends you might have, or drug dealers or the lebanese gangs as they always have "friends who might know a friend, who might know a friend.." who can sort you out.
Bear in mind that these guys would be too intelligent to organise an "event" as the chances of getting busted with a whole bunch of herps is pretty high and the penalties would be far more severe than getting busted making a swap for a single reptile at a neutral location.
Have also read that you can ask dodgy, smaller, pet shops. If you have a large network of friends who keep pythons, chances are, one of them will be offered an exotic at one point or other. If you make it known that you might be interested in one, it won't be long before someone offers you one.
I would like to add that all this info is what i have gathered through online forums and from friends in Australia. I have been overseas for some years now and have no idea how things are in this present day. I have owned what people would term exotics but never in Australia, just overseas.