If you know the version you need, it's easy.
Current PC version:
http://kindleforpc.amazon.com/41022/KindleForPC-installer-1.12.41022.exe
Just change the version numbers, because Amazon
does leave the old versions accessible.
So... I assume the same will work for a Mac, the latest version of which is:
http://kindleformac.amazon.com/41015/KindleForMac-41015.dmg