I'm normally a diet coke addict but I will be about 4 months pregnant when we do Disney in May so I figure I better plan to behave at least part of the time!
At least this tells me there are some options for caffeine free w/o the calories. (I can drink WAY too much pop. I'd weigh 500 lbs if I drank regular coke!) I am actually sort of 'off' the pop right now, but if my last pregnancy is any indicator, I'll be wanting it again by May.
They have it at about half of the TS places and most of the resort food court locations. They don't automatically say they have it you have to ask because they just say diet coke when they list off the drinks. So if you want caffeine you should ask as well.... Many locations also carry the Minute Maid Light which is also sugar free and caffeine free.
I had it last yeart at Boma at AKL. Our server brought it out in a can with a glass of ice, so I'm assuming it was from the bar somewhere. However, it did not cost me anything - came as my drink with the DDP. Good luck!