Copyrights

[thoppil]

I have a question regarding the copyrights of old music. I know that people like Bach, Mozart, and Beethoven no longer have copyrights on their works. (I'm not sure if copyrights were invented yet.) But what sources do you use if you want arrange some music of, for example, Bach for an odd ensemble? I wouldn't think I could use something from this site since I assume Virtual Sheet Music or Fabrizio Ferrari owns the copyright in some form. Does that mean that I would need to find a copy of the music that was published some 100 or more years ago?

I would appreciate any help with this.