Thank you for the suggestion.
Here is the website for the M250 sleeve bearings
https://www.igus.co.uk/product/68 I don't know the correct dimensions at this stage, I was looking for the site as I was curious. I'll measure up my late Kanguro swinging arm bushes tomorrow and see if there's a likely fit for one of the permutations. They're reasonably priced (5.04 GBP for MFM-1824-30, which seem to be the dimensions 18mm inside diameter, 24mm outside dimension, 30mm long), which is my initial guess for what might well suit.