Ringing Forums

I don't know if you can buy the rollers directly - they are usually provided by bell hangers. You can find a list of those in the 'Specialist Services' chapter of Belfry Projects. (https://belfryprojects.cccbr.org.uk/115-specialists/). You may need the services of the bell hanger to install them, as they may not fit easily into an existing pulley box.
A major advantage of plastic rollers is that, being lighter, they put less drag on the rope as it reverses direction on the ground pulley. Perhaps I should add that point to Belfry Upkeep!

Oops, that link should have been: https://belfryprojects.cccbr.org.uk/docs/115-specialists/

A quick Google search for 'plastic pulleys' brings up several pages of suppliers - from your local Screwfix depot to many specialists pulley makers.

Those living near the coast needing pulley blocks for rope guides can obtain smaller sizes from yacht chandlers. Larger sizes - e.g. for the ground pulley below the wheel - would most easily be sourced from a specialist supplier through the foundry or bell-hanger.

The plastic pulleys for bell installations are bespoke for the application and you're not going to find them in a general industrial suppliers product catalogue.
The majority of them are the Whitechapel design with twin bearings on a 1/2" bolt from the 1970s, which are 1.5" or 2" wide, along with a variety of diameters from 5" up to 8". If you get the right size, they're all interchangeable from the current suppliers (Whites/Nicholsons/Higby) as they all use the same design of fitting, but some are lighterweight than others, the lighter ones the better.

There was an era where Eayre and Smith were supplying plastic pulleys to slightly different dimensions to those listed above (they were narrower) and sometimes they even fitted plain bush bearings. These are no longer available and are either require a new pulley box or a timber one being turned up bespoke.

I fitted plastic rollers into a belfry some years ago. They were sourced from Whitechapel Bell Foundry, so you would need to find an alternative source of them. We were able to fit them in place of solid wood rollers running on plain bearings within the original pulley boxes, though we did have to adapt the boxes slightly to accommodate the wider pulleys.
The changeover improved the bell handling immensely. They have now been in service for a number of years and we continue to be happy with their performance. Like any mechanism they do need to be checked regularly..