For some reason I can't find Cakewalk Sound Center and Studio Instruments series allthough I had them installed earlier this year because I made projects with them (in Sonar X3). Maybe this is due to an update.
 
How do I reinstall Cakewalk Sound Center and Studio Instruments series?

Have you check the directory
 
%install drive%\Program Files\Cakewalk\VSTplugins ?
 
If they are not there then you should be able to run the install program do a custom install and only select the missing bits.