Dropbox apps for Apple or Android TV

You'll want to look into what's known as "side-loading". There are dozens of Youtube videos out there on how to do it, but basically you need to get the APK file (Androids version of an EXE or an installer) from the phone version. You can download this on your PC from the browser version of the play store and putting it on a flash drive to get it to your Android TV. Android TV has an app that called ES Explorer that is a file manager you can use to install the APK (just open it). Before you install you will need to enable apps from unknown sources in the security settings. After you do that you will need an app called "sideload launcher" in order to view any apps that are not from the play store. It will be in that app automatically if it is installed. And there you have it. 

It sounds complicated the way I explained it, but it should not take 10 minutes even, and this process is very useful for any other android phone app that you wish to run on android TV.