Here, i found it: github.com/CGCookie/blender-addon-updater though it looks like it only works with github which makes sense because I don’t think blendermarket has an API
A couple years ago there was a discussion about that idea on Right Click Select, and before that, cg cookie made (now outdated) script for update checking.
However, there are no current resources that I am aware of, which is a shame, because it would be really handy.