That would be the C208 (Cessna Grand Caravan).
The UN might not be the most proffesional crowd when it comes to aviation but for those looking to build time and learn a lot its a good place to start. Who we kidding, its one of the few places where a relatively low time pilot can still get a job. (If he is prepared to put up with deepest darkest and everything it has to throw at you).
From the above posts you will see that the South African contract companies are responsible for the bulk of Western aircraft plying their trade up North. These are the guys to get hold of, and with enough determination, you should eventually get lucky.