With the release of latest developer preview 3 of Android M, Google confirmed that Android M is indeed Android 6.0, and that it would be called Marshmallow. The latest preview build already show Android 6.0 as Android version, in place of Android M from earlier build.
While Android 6.0 is yet to be released, at least we can have some of the Marshmallow’s stuff already for our regular Lollipop devices.
For those interested, find the Marshmallow wallpapers here. While, here is your download link for Android 6.0 Marshmallow ringtones. There are 8 alarm tones, 11 notification tones, 12 ringtones and 25 UI tones zipped into one file.
Find here more ringtone packs of other devices and OS.