Help on uninstalling Backup Exec 12.5

I have an install of Backup Exec 12.5 on a system running Windows Server 2003 (32bit). I am attempting to uninstall it, but am receiving an error on uninstall. That error states, "The installation source for this product is not available. Verify that the source exists and that you can uninstall it."

This install of Backup Exec predates my arrival at my company and the outside vendor that installed this product on this server is not reachable. I suspect if I can grab hold of the install files I can use that to uninstall this software, so my question is - Where do I find an install for Backup Exec 12.5 that I can download and use or is there another way I can uninstall this product without having to manually every file and registry entry associated with Backup Exec?

Thanks!