Fusion installing Mavericks this item is temporary unavailable
The only 'official' way to get 10.9.x [which would actually be 10.9.5] is to have previously 'bought' it - it would then be in your previous purchases list on the App Store &amp; could be re-downloaded. 

Alternatively, if that was the OS that was on the machine when new you can get it via Internet Recovery.

Otherwise, the only OS available to download will be Yosemite.