Hey I found this post while researching the same story and there is nothing online!
I heard it was shortly after the end of World War Two but Japanese scouts were not reinstated until 1950 and missed the jamboree of peace in 1947.
The story is important to me because of the lesson of patriotism and solidarity, so I’m hoping it’s true.
Since posting this, have you @skeptic learned anything new or do you care to corroborate?