Flappy Bird, we hardly knew ye. But all is not lost dear iOS and Android users, as it just so happens that Flappy is still alive and well on the Internets.
All you need to do is look for the IPA/APK files, download the ZIP or RAR (or whatever format you get), and feed the game to your handset. It’s much easier on Android because all you need to do is drag it to the Downloads folder, but iOS requires you to jailbreak the device.
Be on the lookout for sites that ask you to complete forms and stuff like that. They’re likely to be scams. In a nutshell, download Flappy Bird IPA/APK files at your own risk.
With that out of the way, I also don’t encourage jailbreaking your phone. However, people are asking about the game, and the topic is hot and up for discussion.