There’s always the Viewer Heartbeat Service (VHS). https://dev.twitch.tv/docs/drops which is available to game developers/publishers that have games registered on Twitch.
It does require the broadcaster to opt-in though, so you’ll only ever get data from broadcasters (and any of their viewers) who have gone through your OAuth process and granted you the ability to track their viewership of your game. Any channel that hasn’t opted in will not be included in the VHS data.
Other than that the only option that currently exists is to poll the streams endpoint with your game id as previously mentioned.