I do not know of a Honda premade extension for the 8HP outboard. I looked in my Sail magazine archive and came across this description of a DIY gear extension design. No idea if it works. If you’re handy with Stainless Steel rods you might be able to get the extension you seek.
D.I.Y. Outboard ShifterA lever for all reasons Although I could reach the tiller/throttle of the five horsepower outboard that was mounted on the transom of my 20-foot trailersailer, whenever it was time to go from forward to reverse I had to face aft and then bend over the transom and the motor...
sailmagazine.com
Looking at the recent models there are basic movement issues associated with shifting gears. These will need to be addressed when you try to extend the motion away from the engine.
I think your gear shift may look like this.
The gear shift lever rotates the shaft to change the gears. You will need to design a mechanical way of rotating that shaft and do it from what ever distance you choose. I note that the further you are away from the gear shift the more exaggerate the current designed motion will be.
This may be why the Honda engineers have not (yet) decided to produce a gear extension. The 8HP outboard is produced to meet the market for that unit. Cost and simplicity were priorities for that unit.
Good luck.