There should be no reason you can't find MP3 files. What version of BearShare do you have?

If it is 5.2 you need to switch to 5.1. See the first post in this thread. If you
already have 5.1 go to Setup/Filters and make sure MP3 is not in the lists.
While you're there, add WMA, WMP, WMV, M4P and ASF to the list on the
right side. Those are the types of files that can be infected with DRM and viruses.