You are on the right path by searching for Android TV through the ping sweep, but with it pairing (especially if it is a Google Cast device) is not as simple as opening socket on port 8009. It uses the port encrypted TLS and Cast Protocol (Protobuf-based). The Flutter/dart does not basically support it. To make the pair properly, you will need to use platform channels and apply a pairing logic using the native cast SDK on Android.

I hope my answer was helpful to you!