Android 4.4 (KitKat) is only available for Nexus 5 (for now), and if you want to get KitKat launcher on your Android devices (running Jelly Bean, preferably 4.2), you can do as follows on your own risk
** Note that an XDA user found this way and you may go to his topic in XDA to ask your questions (Click Here)
1. Download the zip file (Click here to Download)
2. Extract the zip and place the apks on your phone
3. Install PrebuiltGmsCore.apk
4. Install Velvet.apk
5. Install GoogleHome.apk
6. Press home button, select the launcher and enjoy!