Here is a link to where you can purchase it: Honda Power Equipment: Honda Generators, Lawn Mowers, Snowblowers, Tillers
I am new to this forum but have owned a Honda 4518 since the early nineties (if I can remember). Do all of my own service and am presently going after a loud grinding noise in the PTO assembly. I assume the bearings & parts will need replacing.
I have gone through a lot of drive belts and have found the Honda belt the best by far in holding up. Costly but worth it as far as I can tell.