If you are on a version that deploys the JuniperInstallerService, you can download the installer from your device by going to Maintenance->System->Installers. If you don't have a test box, you may have to upgrade, download the installer (.exe or .msi or both) and then downgrade in order to get the installer package for the new release. I would recomment contacting the JTAC since this process depends on your current version, and the version to which you plan to upgrade.
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