There is a converter somewhere here in cyberspace, and there are some articles about converting music on the j2o site, but Jazz2 can also play music files with .mod .xm .s3m .mtm extensions. Converting them just takes time and gives the same results. (Do correct me if I'm wrong, because I think that the filesize matters.)
And converting the files into .j2b files makes them unreadable for mod-players.
If you're meaning to convert an mp3 file to a .j2b format, forget it, thats way too hard and time consuming.
You can download music and trackers at modarchive.

As for the tilesets.... I don't know...