Mark, yes they have CITES tags. I am unsure about ANYTHING to Australia, will find out for you. (As far as I know, you are not allowed to import elephant, but croc I honestly do not know.)
JabaliHunter, I am not sure what you mean by best time, do you mean most popular? I have shot very good trophies of both right through the trophy hunting season, which runs from February to November in Namibia. The cooler months, end April to end August are most pleasant though. It heats up a lot after that, but I did have a group of Spaniards shoot 289 springbok last November, so it can be done effectively the whole season.