I use easynews.com (they make everything VERY simple for $10 a month), but check out this site:
http://www.newzbin.com/
It will tell you what was uploaded, when, and in which groups.
You could then go to those groups and search the files. It also depends on the newgroup reader you use. I personally use Forte Agent (which is perfect for joining large uploads).
One MP3 might be split over the span of several different postings, so you'll have to join them manually if your reader doesn't already do this.
For example, subjets will read:
"Blah.mp3 [1/5]" - 500k
"Blah.mp3 [2/5]" - 500k
"Blah.mp3 [3/5]" - 500k
"Blah.mp3 [4/5]" - 500k
"Blah.mp3 [5/5]" - 398k
You join em together so it downloads in one part instead of having to piece together each individual one.