You may be able to purchase a download code or otherwise directly get a copy of Mavericks full installer
from Apple support, although perhaps not; some computing hardware cannot fully use the newest OS X.
As various users attest, there are issues in certain models where their upgrade is limited in hardware so
the full functionality just isn't there in a newer version. And of course, some costly third-party software
may not have been upgraded to run in the newest OS X; or may require a new major investment to do so.
If you can determine ahead of a visit to an retail Store with a Genius, that they could in fact be of help,
then a trip may be worth the trouble. A support tech may have a means of applying a replacement 10.9
OS X version that does not have an AppleID associated with the file; or may have a 'tech ID' for this use.
{And to get a used computer, such as those I've seen on craigslist, with screenshots of El Capitan running
and a new hard drive installed, have no original Recovery partition to attempt to retrieve Mavericks.}
Some graphics cards and other hardware are marginal past 10.10, or 10.9.5. Among those, Mac Mini
has more than a few issues even with the Late 2012; while a firmware update may help those, none yet.
Without Yosemite available as intermediate step, those going from 10.9.5 to 10.11.x found troubles there.
To be able to purchase a special version flash USB of these older OS X versions to include with an older
Mac when it goes into the used resale market, would be a fair idea; since no telling what may be available
at the Mac App Store in five to seven years. I'd like an offline option to restore an OS X when there are no
system discs, to prepare a Mac for a new owner or reuse. Not everyone has great bandwidth or fair internet.
And once an older computer gets so far along, for some it's better to leave them at a 'standalone' status. 😐
edited 4x due to network issue & interference here