As far as I know, there are no download sources for ‘forced’ subtitles.
I can only recommend you to make yourself familiar with the “peculiarities” of makemkv to extract them from the disc.
Makemkv will extract the forced subtitles and write them into a separate subtitle stream in the produced MKV file.
Stupidly though, it doesn’t set the ‘forced’ flag on this subtitle stream.
So it is up to you to identify which subtitle stream contains the ‘forced’ subtitles and then to set the forced flag accordingly.
Get yourself some software tools for this task:
- Makemkv
- MKVtoolnixGUI
- Subtitle Edit
- and very importantly: mediainfo
(pay attention during installation, it comes with a ‘piggybacked’ installer which asks to install additional crapware. Make sure to set/clear the right checkboxes!)
mkvtoolnix is for setting the ‘forced’ flag in general for all things manipulating or making MKV files
Subtitle Edit helps you extracting subtitles from mkv files. It will display them, and you can perform OCR on them to convert them to the more Plex-friendly SRT format.
mediainfo is a fundamental tool for anyone who wants to know what’s inside of video files
When you open an MKV file with Subtitle edit, it lets you choose which subtitle stream to look at.
In the worst case (if there are several subtitle streams in the file) you have to try all and then pick the one with the least number of lines.
(Since the number ‘forced’ subtitle lines is usually much lower that those of ‘full’ or even ‘hearing impaired’ or ‘commentary’ subs.)
