Is there a valid way to get private photos from snapchat? Some kind of leak website or whatever?
Nope.
There used to be 3rd party snapchat clones and 3rd party apps that could serve as an interface for snapchat but those got shut down and Snapchat locked up its API so only the official app can access data now.
Any leaks are going to be from individual people having poor password protection rather than some kind of general database exposure.