International Koi Show? You mean with people flying in koi from all over the world for a show? It would have to be a country virtually no customs so the koi could come through fast and it would have to be a country with lots of flights in and out. My guess is it would need to be when most of the people that you would try to get to attend have time off so summer.
Hawaii is centrally located with lots of flights. Not a bad place to go either. Weather is always nice, but you guys would not want to pull fish out of your pond during the winter to go to a show. Everyone would have to get a $5 importation permit ahead of time. However, its a small community and once the situation was explained to the agricultural inspection folks and they were brought into the process, it would go smoothly.
I would think that whatever country you choose would have to have a lot of locals that are into koi keeping to fill in the gaps for the show. Canada has quite a few koi keepers but the season is real short so you have a narrow time frame for the show. Hawaii is certainly a decent choice. Pretty sure there are lots of koi there and would be a big draw based on the exoctic location. The real shame of an international show is that the Japanese could not participate unless they were going to sell off whatever they brought to show as they cannot bring koi back into Japan once they leave.