If he is looking for the 3rd or more disc, the program is already installed likely and just needs to copy the sounds library to the installed path.
I would also post this on the Toontrack forum to see if they can help at all. Maybe support could setup a download for only the files you are missing? Post your issue up in the TT forum and I am sure someone will give you more advice.
I would try to clean/resurface/polish the DVD first though. The disc doctor products work pretty good and you can reuse them on other DVD/CDs but don't use them on Blu-Ray discs. Don't ask how I know about that one...