The valgrind release archive at http://valgrind.org/downloads/old.html does not list release 3.5 or anything newer (which would be up through 3.12.0 as of today.)  Old releases are useful for forensics (would a particular bug have been detected by last year's release?) and for studies of software history.  In theory a complete source code revision history tree can provide all the answers, but "there's many a slip twixt the cup and the lip" in making an actual release.

File storage space is a consideration: 14MB per recent release.  Other organizations have offered space and set up their copies (https://sourceware.org/pub/valgrind/ as of today; thank you Mark Wielaard.)  If valgrind chooses not to maintain its own archive and page of links to it, then a polite reference to such known friends would be appropriate.