It's available on the PURCHASES tab of the Mac App Store if you've ever downloaded it to any computer associated with your MAS account. At this point, I am not sure you can get it otherwise.
If you haven´t downloaded it previously you can´t download it anymore from official sources. You can try a internet recovery if your computer shipped with it, otherwise you will have to look for it on your favorite torrent site.
I don't recommend using torrent sites because you could end up with more than you bargained for...
If you have a friend who has 10.9 you could ask for him/her make you a 10.9 installer, with these instructions.
If you have some software that won't work on 10.10 or 10.11 you could try contacting Apple support and politely explaining your situation. There is no quarantine that they will make an exception but it won't hurt to try.
You might also want to try search, there are a quite a lot of discussions about this topic in Mavericks and OS X forums...
If you have a nearby Apple Store they should be able to copy an installer to a USB drive for you. Downloading an installer from an unofficial site is not a good idea.