[vrushank7387]

I like the short, in-app tones of the Facebook Messenger app. Is there any way one can download these files for use as custom tones?

[dKp1977]

I would check ZEDGE? Ringtones & Wallpapers | Windows Phone Anwendungen + Spiele Store (Deutschland)
There are several ringtone/notification apps in the store. I'm sure many of them provide the sounds you're looking for.

[Abhishek P]

I use melodia, it's also really good