I believe the only sources now are third-party APK sites. From what I understand APKMirror is one of the most reputable of those, as it's run by Android Police, a major news site for Android. They have Retry available: https://www.apkmirror.com/apk/rovio-entertainment-corporation/retry-2/retry-2-1-5-0-release/retry-1-5-0-android-apk-download/

That said, I can't guarantee that this or other APKs are 100% safe. It's a fantastic game, though, and personally I'd trust that site.

Let us know if you get it installed!