Dial spring insulators/bushes

[els]

Hi All, I have a couple of old GPO (UK) dials but the little insulators on the springs have gone missing. They appear to be a tiny bit of tube made of some kind of Phenolic fiber paper. Does anyone know of a suitable replacement? I've searched everywhere but I can't find anything at all. Any help gratefully received.

Have attached a pic and circled the bit I mean.

Thanks