If ypu create a SlowBlues Magic GarageBand project and save it, it will contain all loops as .caf files.
Ctrl-click the project package, select "Show Package Contents", open the "Media" folder inside. You will see all loops and can listen to them to find the correct one.
In GarageBand you can simply drag these caf to the TimeLine, like audio files; probably you can do the same in Logic.
For example the "Brushes" loops from "Magic GarageBand: Slow Blues"
There is a more elegant solution than digging in the Package file.
First you have to know that GarageBand and Logic share the same Apple Loops, meaning they access the same Apple Loop index files. All the Apple Loops that you see in your GarageBand Loop Browser are also displayed in Logic' Loop Browser. The problem in your case is that the loops used in the Magic GarageBand Projects are not listed in the Loop Browser.
Simple solution for that:
Open the Magic GarageBand song as a GarageBand Project. Now you see the "blue" Apple Loops on the Tracks. Just select any Loop and choose the Menu Command "Edit > Add to Loop Library". Give the Loop a proper name and proper tags and click "Create". This will save that Loop to the Apple Loops Library under "My Loops". Now when you launch Logic, you will see that Loop in the Loop Browser and you can drag it right into your Logic Project.
ALl the file management is done only in the application (GarageBand and Logic). You don't have to navigate or search in the Finder or drag files from or to the Finder. Everything is done through the user interface in the application.
Hope that helps.
<Edited by Host>