The JCPDS (now ICDD) database license can be purchased at www.icdd.com
If you are just looking for a free standard pattern for Mn2O3, you can try the COD (crystallographic online database) at http://www.crystallography.net/cod/
Yuxin Liu if the patterns don't match it may be because you are comparing different oxidation states. You could have MnO2, Mn2O3, or Mn3O4 - each of these has a different structure, so you really need three cards to determine this.