Do they have to be genuine Honda?
If not, they're a pretty generic thread and you should be able to find them in Screwfix Direct or your hardware store of choice!
Possibly go to a yacht dealer and get some stainless ones...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball