It is possible that the plug-in has not been scanned correctly.
To force a re-scan of the plug-in, do the following:
Go to Logic Menu and go to Preferences > Audio Units Manager.
Click Reset & Rescan Selection.
If problems persist, quit Logic.
HD/Users/'Your Account'/Library/Caches/AudioUnitCache In that folder, delete the file called "com.apple.audiounits.cache".
Restart Logic. It will re-scan all the available plug-ins, then the plug-in should now show up in the list.
If you do not see the "User Library" folder, you may open this path in a new window by clicking Go > Go to folder... in 'Finder' (the shortcut is SHIFT+CMD+G), and type in the address in the window. Or...
Open Terminal in your Applicatiosn/Utilities folder and type the following command, enter your system password and press the Enter key. This will show the folder permanatly.
chflags nohidden ~/Library/