Since Apple no longer lists Mavericks on the primary Mac App Store search, you may need to use these verified external repositories:
Today, users primarily seek of Mavericks for legacy hardware restoration, virtual machine testing (like VMware or VirtualBox), or creating bootable installation media. Quick Download Links for Mavericks 10.9 mac os x mavericks 10.9 iso and dmg image download
Advanced users can use a terminal script from Mavericks Forever to fetch installer images directly. Since Apple no longer lists Mavericks on the
Hosted as a 5.7 GB optical disc image, available at the Internet Archive (10.9.5) . mac os x mavericks 10.9 iso and dmg image download