It's my app that I never published to the Google Play Store and then foolishly deleted the source code. So there is no way to download it from a site and no copyright infringement.
The app is on an old phone I have and I'd like to be able to fix it up in Android Studio and put it on my new phone.
I've been looking everywhere on Google and on this site but I can't find the right combination of search terms.
Try using some tools to decompile it like Android Apk decompiler