The Panama Papers were not leaked at all. They were handed over to a German media company which probably paid a good price (translation/summary here) for that deal.
This means, the panama papers generate a lot of media attention, and probably already paid off for the Süddeutsche Zeitung but it wont have much impact as long as the full papers are not completely published at all.
WikiLeaks already asked the rhetoric question on Twitter, if they should release the full papers. Which is a rhetoric question trying to make people aware that nothing was leaked yet. And Wikileaks can't leak anything at all, since the 'whistleblower' decided not to leak to the public but to sell to the media. That's a huge difference.
So far, the SZ never leaked any documents (0). Instead, the guardian leaked a total of 2 documents.
Out of the roughly 11,500,000 documents, only 152 are available currently on document cloud. Not much more was really leaked so far.
To answer the question more directly, the Panama Papers including 11.5 million documents and 2.6 TiB in size can not be downloaded anywhere.
The best you can do is hand-picking the few released documents out there or wait until someone from inside the media company leaks the full dump.