Because this is a release, it follows a standard frame rate (usually 23.976 fps). When searching for subtitles, look for files tagged with "BluRay," "720p," or "YTS."
Keep both the video and the .srt file in the same folder. subtitle Lake.Mungo.2008.720p.BluRay.x264.[YTS.AG]
You can find community-uploaded subtitles on major repositories: Because this is a release, it follows a