We've got a couple of chandelier lights that take normal BC candle bulbs.

There's a white plastic shroud, with immitation candle grease running down,
that fits over the bulb holders but after a few years these harden, crack
and disintegrate. They are about one and a half inches diameter and 3" long.

I've tried several larger stores that used to carry these years ago but now
they don't (e.g. John Lewis )

I've tried searching on Google without success but this maybe because I
don't know the proper name for these things.

Does anybody know what these things are called and where I can buy them?

Any help appreciated.