So a 50K pot is a very common item. However finding one with exactly that mechanical configuration will be quite difficult, IME.
You would be FAR FAR ahead of the game by trying to clean the pot. Finding replacements for weird mechanical pots like that is a nightmare.
Since it is a single section pot, and your "sound system" is 3-channel ("2.1"), it is almost certainly creating a DC voltage relative to the knob position and the gadget is using some other method to actually control the audio volume. There is no way that pot is actually controlling the audio signal directly, so it is very UNLIKELY to be a log/audio taper pot. It is almost certainly a LINEAR pot.
OTOH, since it is only creating a DC voltage, the actual resistance value of the pot is of almost no significance at all.
I wouldn't want to use anything lower than 5K ohms or higher than 100K ohms. but anything in that rough range would likely work fine.