have you tried to search for all your GarageBand projects using the search function of the Finder?
Open a Finder window and enter the keyboard shortcut ⌘F for "Find". In the window that opens, set the "Search:" to "This Mac" and set the "Kind" drop down menu to "File Extension" and enter ".band" into the search field. Then press "return".
this should show you a list of all GarageBand projects that can be found on your Mac.
If you select one the files that have been found, the path to the file should show in the footer of the panel.
Yeah, I tried to search and no luck.
The files were in the default garageband folder, as you say, Christoff.
I doubt it was itunes, even though it seems to have disappeared around the same time as the major itunes update and was there for a long time before that without trouble.
This is going to require an undelete process as the files are not anywhere on the system, but I can't find info about recovering garageband files. I've tried a recovery software, but it seems to find everything BUT the .band files. Maybe there's another way...?
Any help would be appreciated.