I don't know about online for the Disney ones. But if you go to amazon and type in "waterproof ID case", they have the same thing...and it's a bit cheaper.
They sell them in water parks, for sure. One is about the size of a pack of cigarettes and there is one with that is roughly the same, but much thinner.
They work well, too. They tell you it isn't waterproof, just resistant...but I have taken mine into the wave pool...and I go to the rope, where you are buried under water...and the money is dry when I'm done. (Now they have those wrist gift cards, which is much better, IMO.)
I think they should sell them everywhere. Those plastic pouches don't hold enough and are difficult to get things in and out of!