Unfortunately, the boot comes with the entire harness. You may want to reach out to some of the NSX-focused wrecking yards like AH Parts. Or, I bet that the boot is common among Hondas of the same generation. How much you want to bet you could find that boot on a Legend or Integra at your local pick and pull?
You can do a passable job with electrical tape if you plan it out. Go over the top first with 2 layers, perpendicular to the side opening, leaving the tape ends along the bottom. Then go along the bottom to cover all of those ends, leaving the ends on the tube for the side opening. Then wrap the tube for the side opening and cover those ends. Use a good tape like Scotch Super 33+ or even 88.
But definitely better if an Integra or Legend part from a wrecker fit. I do remember looking at Amazon & the like for something that would substitute without success.