xvfrona wrote: The Honda dealership reckons the piston is 0.5mm under size at 53.5mm and is having trouble finding the correct rings. Anybody got any suggestions as to what these pistons might be from or where I could get rings from? There are no stampings or markings on the piston anywhere.

The dealer has got an eyesight problem!

They cant be 53.5mm more like 53.95mm.
.5mm is about ten times the normal clearance.
If they are pre 95 RS pistons and rings you are out of luck as Honda dont make them anymore.
Your only hope is to find some old stock
or put NSR pistons and rings back in.
Good luck!