GarageBand does not support exporting midi, sorry.
But all the loops you create and save as loops will be placed at either of the following locations:
- /Library/Audio/Apple Loops/User Loops
- ~/Library/Audio/Apple Loops/User Loops
Note: The tilde (~) represents your home folder. To get to this location, in the Finder, choose Go > Go to Folderfrom the menu. Type ~/Library/Audio/Apple Loops/User Loops in the "Go to the folder" field and press the Gobutton.
Whether they go into the home folder path or the system path depends on the "My Apple Loops" preference you have set in the Loops pane of GarageBand preferences.