In June, Apple added the last of the G5 models (late 2004 towers and 17/20” iMac G5s) to their Macintosh “vintage” list for the U.S. Apple also changed the status of the remaining G5 model lineup to “obsolete” for all other areas of the world.
If you purchased a G5 outside of the state of California, there is no difference between vintage or obsolete. In either case Apple is no longer providing service, nor can service providers order parts.
If you purchased a G5 in the state of California, a statute forces Apple to offer service and parts until the product has been discontinued more than seven years. http://support.apple.com/kb/HT1752