The default location is
C:\Program Files\Cakewalk\Shared Utilities\Internal\ProChannelConcreteLimiterThe actual location depends on where SONAR was installed. Usually the "Shared" folders are on the same drive with the program.
It probably does not matter where the Concrete Limiter is installed as long as it is in the scan path. Pretty easy to add the actual path to the scan path in Preferences and see if it works. The fact that the plug-in was not automatically picked up with the rest of the PC modules is unusual.
FYI, the forum will soon go read only. Please read
http://forum.cakewalk.com/FindPost/3806006