JCPDS files can be found in archive software available from the ICDD (http://www.icdd.com/) .  Their software is not free, but there is very reasonable pricing for academic institutions.  Depending on what materials you are investigating, you can find some sites where people are voluntarily depositing diffraction files for free download.  Two such places are:  http://www.crystallography.net/cod/   and  http://comptech.compres.us/tools/jcpds/.  Unless you have a very complicated mixture, it is often enough to make a visual comparison.  And, the software you use to collect data often has a comparison feature built in.

http://www.crystallography.net/cod/ is more suitable