Copyright law expressly forbids the copying of scores. There are exceptions, but these are clearly and narrowly defined. They include, for example, the copying of works that have been out of print for several years and no longer commercially available; they may be copied, but only if the publisher's fees are paid.
Buying scores in any quantity and making copies for rehearsal is not permitted by law. This and many other forms of the copying commonly seen are illegal.
Please be aware that copying scores is a criminal act that causes massive damage to the publishing and book retail industry in Germany and may well lead to its eventual disappearance. For more information about this topic, please check out the Verwertungsgesellschaft VG Musikedition website.