Unfortunately due to legal reasons Veritas can no longer provide the SDR disk as a pre-created download.
This is covered by this document
http://www.veritas.com/docs/000109525
Any Backup Exec 2012 customer that does not already have the SDR disk downloaded and intends to use SDR will have to upgrade to a later version of Backup Exec where you can make an SDR disk directly without needing the downloaded ISO.
Any Backup Exec 2012 customer that cannot upgrade (and does not already have an SDR disk) will have to use manual DR processes (where you re-install the operating system with same name and ip address into a workgroup and then install the required BE components to do the restore)
Note 1: Backup Exec 2012 is in EOL status and support is already limited as such this legal SDR limitation in conjunction with the support status for that version should justify planning an upgrade.
Note 2: Any 3rd parties that provide copies of the BE 2012 SDR disk are potentially also in breach of the legal terms and conditions for the distribution of WinPE