Hi Peter
We (Richard Heenan and I) have a component that we use for the LoKI benders (attached) which was a modification of the Pol_bender component to allow us to have it bending downwards/upwards and still have functional gravity. This allows for different reflectivities and is truly curved as well as giving a curved representation in the model.
You can find our LoKI model on bitbucket (link below) if you want to see how we use it.
https://bitbucket.org/essloki/loki-mcstas-master/src/master/
Cheers
Andrew