I bought new bandwheels for my Startrite 352 from this chap Harry
Hayward gbservicing @ hotmail. co .uk (get rid of the spaces) - very
reasonable prices

He runs a very small spares business, but bought up the old tooling to
make bandwheels for Startrites.

I'm sure he will be able to help or offer tiptop advice.

When you say "broken plastic top wheel" - bandwheels are usually
aluminium (cheapies), steel (midrange like mine) or cast iron (good
ones) - did you just mean the rubber tyre?

I believe there are companies specialising in fitting new tyres to
bandwheels - start off by contacting woodworking machinery suppliers.

Otherwise many of the traditional British machinery manufacturers
still offer support on all their products since they equipped Noah.