for GarageBand 6.0.5 from its public download pages. Here is how you can still access it: Apple Discussions Mac App Store (Previous Purchases):
GarageBand 6.0.5 is an older release of Apple’s GarageBand music-creation software, part of the iLife ’11 suite. It includes bug fixes and compatibility improvements for macOS versions available at the time of its release. Garageband 6.0.5 Download
If you previously owned GarageBand '11 (version 6.x), you can usually re-download it from the tab in the App Store. Internet Archive: for GarageBand 6
So, why should you download GarageBand 6.0.5? Here are some benefits of using this powerful DAW: Garageband 6.0.5 Download