Old JasperReports releases can be still downloaded from SourceForge.net, although they no longer appear in the list of JasperReports releases. To download an old release, one can use URLs like the following:
http://sourceforge.net/project/downloading.php?group_id=36382&filename=jasperreports-0.6.8.jar - for the binary release/jar
http://sourceforge.net/project/downloading.php?group_id=36382&filename=jasperreports-0.6.8-project.zip - for the source/project release
(Substitute 0.6.8 by the release you want to fetch.)
Alternatively, one can check-out release tags from the JasperReports SVN repository; a user registered for the development area of JasperForge.org is required to access the SVN repository. Release tags are located under the "tags" SVN folder.