If a piece you want to perform is out of print you should contact the relevant publisher and ask them to print you a copy (if you’re not sure who the publisher you can contact the Music Publishers Association). The publisher then should let you know within three weeks if they are able to supply a copy or will allow you to make copies for your group. The publisher may decide to attach conditions to this permission. If the publisher allows copies to be made a fee should be expected as the publisher will usually need to pay royalties to the copyright holder.
Occasionally a publisher will refuse permission to reproduce the work. This may be because the work has been deliberately withdrawn by the composer or for copyright reasons. In these rare instances you will not be able to obtain a copy.