Since the official title of the movie is Kanchana (2011) (known in Hindi as Muni 2: Kanchana), but you have specifically typed "Kanchana 3" and "mm sub", I have broken this guide down into two possibilities to ensure you get exactly what you are looking for.
The Cinematic Impact of Kanchana 3: An Analysis of the Horror-Comedy Formula kanchana 3 mm sub
Warning: Avoid any site that asks you to download an ".exe" file or a "subtitle downloader" software. Legitimate subtitle files are only .srt, .ass, or .ssa (text files under 200KB). Since the official title of the movie is
If you have a standard BluRay rip, YIFY subtitles sync perfectly. Look for the tag YTS.MX or MM. Indicated only if 3 mm causes symptoms AND