Did you try searching your hard drives and backups for "Multisamples" folders?
 
If you never deleted them, you may have more than one, but the registry can only point to one. This was why re-assembling those helped me in my post above. I had installed it (and other sample offers) in different places, but still had them all.
 
As for the installation files. I would check your CW store account for the DimPro 1.5 installation files (is a separate install). I am not sure which version you are running, but X2 and X3 DP installs are the same (unless you have different versions between the two (studio/producer, etc.)