Housing grommets for speaker/bell wire

There isn't a particular section for this type of question, sorry.

I have an enclosure which will have thin bell wire coming through it and I need a 'grommet' to ensure the drilled round hole that passes the wire has no gaps (due to an epoxy filling process) and also to give the wire some flex protection. I've began a search and I'm really not coming up with any hits, which probably means there's another term for them. Any illumination on the matter would be much appreciated!

You need better specs than that. I did get some really small ones somewhere. e.g. about the size that you would see coming out of a wall wart.

A cable gland with strain relief would give the best combination of sealing and long term flexing life:

A plain cable gland is smaller and cheaper

You can get classic style rubber grommets with strain relief sleeves, but I can see that filling with epoxy.. It may be OK if you add a bit of self amalgamating tape to the cable and pull that in to the grommet from the inside of the box, to form a flexible plug?

This style used to be very common on power cables at one time:
Again, I'd add a turn of SA tape to the cable where it is gripped, to give a flexible seal.

The problem I can see is that anything very short "along" the cable, like a simple grommet, will have a sharp transition from solid material to nothing, so a very short stress area when the cable is moved around.

You could add a length of heatshrink sleeve to the cable where it passes through the enclosure wall and whatever seals it, with a couple of inches outside as a long strain relief.