Honda MRV/Pilot speed buzzer is part of many buzzer in your car like door ajar, seat belt warning and headlight chime etc. Only possible way to disconnect it to cut the wire as there is no easy way or fuse to disconnect this because its integrated thru main ECU.
Over speed sensor wire is in dark blue color, it is in the main OEM radio connector. Its the 4th wire from the right of that connector.
However i am not very sure if you cut this wire, it will disable all alarm like headlight / door ajar etc or only overspeed one. If you are very desperate in case you do drive everyday long hours on highway then i suggest go ahead and cut as an experiment and you can always join the wire, what the heck.