Ok two things..
Did you follow my instructions and do a search for one of the missing files (Spotlight search or better yet, download EZFind and use that). The installation takes old files and moves them to an unused folder sometimes with "old' in the name. At least give this a try
The instruments you are looking for are NOT part of the new installation, as you've found out, they were from a previous GB or Logic installation.
No, not the Logic Installation Discs. Leave the Logic Install Discs alone now - Forget about them
You need to find your O.S Install Discs. The Garageband Application is usually on the Operating System Install Discs as an included Application.
Get those discs, but DO NOT run the Intallation.
1. First Download Pacifist
2. Use Pacifist to open the Intall Discs and locate the Garageband Files.
3. Then find the Folders - Hybrid Basic and Hybrid Morphs
Those are the files that you need to re-install to make both Garageband and Logic Instruments complete again.
.pst files should be found in
Hard Disc/Library/Application Support/Garageband/Instrument Library/Plug-In Settings/Hybrid Basic
Hard Disc/Library/Application Support/Garageband/Instrument Library/Plug-In Settings/Hybrid Morph
Take a look on your Hard Disc and see if they are there at the moment.
If not, locate them with Pacifist and restore the folder with the .pst files
Sampler Files may have also been messed up. Drum Kits tended to vanish for many people. So check Garageband and see if your Drum Kits still play - if the files are missing - all MIDI notes will just sound a nasty pitch noise that will give you a headache : ) HipHop Kit and Dance Kit vanished for most people.
Hard Disc/Library/Application Support/Garageband/Instrument Library/Sampler/Sampler Files/Dance Kit
That's where the .aif Files should be - If they are not there, restore those folders
Also check for the .exs Files in their Folders . . . example
Hard Disc/Library/Application Support/Garageband/Instrument Library/Sampler/Sampler Instruments/Hybrid Basic
Hard Disc/Library/Application Support/Garageband/Instrument Library/Sampler/Sampler Instruments/Hybrid Morph
That's the essence of what you need to do. It's a lot of cross referencing but if you want Logic and GB to play as it should . . . it has to be done.