You should contact JTAC with your support contract or your Serial number for the switch. The download site for software seems to not have that file readily available, hence you may need to get that version from support. On the other hand, have you tried the Juniper recommended versionand experienced problems with it? If yes, you may want to test the later versions. I know there can be bugs in some versions, but you should also look at the release notes for each version and see what is new/resolved/unresolved etc.